There are three avenues to getting a PortaCount: eBay, or, if you're in the US, government auctions and Craig's List.

Personally, I haven't had much luck with Craig's List, but who knows, you might be luckier where you live.

Regardless of which avenue you choose to buy a PortaCount, here are some things to keep in mind:

• When buying on eBay: DON'T make things worse for others by overpaying. Always check 'completed listings' and 'sold listings' first. Unless you're buying an 8030 or newer, in which case, go nuts. (Note: If you're buying an 8030 or newer, the alcohol cartridge and N95-Companion sections do not apply to you!)

• Calibration date: Very important. It's found on the bottom of the PortaCount, and ideally, it should be dated 2015 or newer. PortaCounts older than this have not been serviced properly, and may have pump damage. A sign it's newer is if the bottom two circular filter covers are flathead screws instead of hex screws.

• Parts missing on the PortaCount: If your PortaCount is missing covers for the bottom two filters, that's pretty bad, and a sign that it might not be working. Avoid.

• The power supply: If your PortaCount does not have a power supply, get a 5V center-positive power supply, with a 5.5x2.5 mm barrel plug. The power supply, to be safe, should provide at least 2 amps, and TSI provides a power supply that provides 5 amps. Power supplies are a commodity, so don't limit yourself.

• Zero Check / HEPA Filter: Zero Check filters are easily damaged, so don't be fooled by fit factors less than 50,000 from an old filter. Just get a new one. Cheapest vendor is ETA, but you can also get them from TSI themselves or even AccuTec-IHS.

• Tubing: If your PortaCount comes with no tubing, or a damaged tube, you could buy new 1/8" ID 1/4" OD tubing and connect it to be sample port, leaving the ambient port empty. That will provide a valid fit test. But honestly, it may just be easier in the long run to buy the three-pack of tubing from AccuTec-IHS for $97. You won't have to worry about the ID/OD tube length, and you'll have two more tubes to prevent build up of condensation. Faling that, you can always buy more tubes from TSI or AccuTec-IHS for $40-45.

• Probes and probe installer: Your PortaCount will probably not come with them, unless the N95-Companion (which will probably cost as much as another PortaCount). Since the probe installer is a standard off the shelf part, both TSI and Accutec-IHS produce them. However, neither are really that cheap, so you might be better off just DMing someone for probes and the probe installer. (Hint hint)

• NEW: Probe Acquisition Tips: Turns out the standard OD tubing the PortaCount uses corresponding standard OD tube parts. The parts you should be paying attention to are: 4mm Stud Push-On Retainers OD Phosphate and Canvas Snap Fastners, 3/8" Post. Note, however, that since this is industrial materiel, you may not be able to get probes for much cheaper than TSI themselves, so better to DM someone for bulk purchases (hint hint, again)

• N95-Companion: ALWAYS buy with the sampling pendant, and the water-trap tubing / headphone-jack like cable. These accessories are a pain to get otherwise (you'll get them from REPSS). And ideally, it should also come with the annoying interconnect cable and a bit of spare ID/OD tubing to connect the PortaCount with the N95-Companion. If you don't have the annoying interconnect cable (or ID/OD tubing), it's not the end of the world, but you may have to DM someone (hint hint).

• Alcohol Cartridge: You can try buying the TSI P-Trak alcohol cartridge (Disclaimer: I have not tested this), or you can go to REPSS and buy the alcohol cartridge from them, for $70-$90 respectively.

• Reagent Alcohol: It's cheapest just to get it from a chemical vendor. Higher purities, beyond 99.5%, are okay. It's just not worth it to get it from the CPC vedors themselves at the moment. It's another commodity.

• Bonus Tip 1: Save money on shipping by only choosing one vendor to supply you with all the missing, obscure parts you need, except for things that are basically common commodities, like alcohol and power supplies.

• Bonus Tip 2: Check if all filters are in place. Use hex / flathead screws on the circular filters, and Philips-head for the rest (NOT JIS, look it up). Be careful not to lift the top too quickly; there's a ribbon cable you need to disconnect.

• Bonus Tip 3: If you plan on opening the N95-Companion, DON'T remove the three center screws. They attach the charged particle separator, and you'll have a hard time putting it back in if you remove them.

• Bonus Tip 4: For PortaCounts newer than the 8020A, the 8030 does not have N95 support. You'll have to buy the models ending in 8. The 8020, 8020M, and all older PortaCounts, do not have N95 support. And as implied throughout /m/CPCSupport, the 8020A requires the N95-Companion for N95 support.

• Bonus Tip 5: Do not buy the 8010. They haven't been serviced since 2001.