My only source is Sam's Laser FAQ...and LPF.
I'd recommend getting a 633nm in the beginning, don't want to get too crazy. There are plenty on fleebay, just make sure it's working. Also try to get the right PSU, with 633 it doesn't matter too much, though it's a good habit to get into for the other wavelengths. If you want to advance, try getting a higher powered 633nm. Some good higher powered ones are the Uniphase 1344P, 1345P, 1345 or the Melles Griot 827, 831/931, and the 927/928. Stay away from SP lasers like the 125A and 127 unless you see it operating. The 125A are RARELY operational. As far as the 127's, SP-127's are often operational, that is if the tube is physically ok and not broken. That being said, the PSU is also questioned, and these don't often meet spec, so it's a bit of a gamble.
Next I'd throw in 543nm. Or GreeNes. They show up, infrequently, in the B/S/T section, and all over the classifieds section of the FAQ. They frequently have 12V PSUs, so keep that in mind, don't plug that into the wall...I've done it, doesn't smell good at all. These are fun when comparing to a low powered 532 because it makes it look a little like colored. Slightly yellower. I've got an 18-24in tube, not too sure, but it's a lot of plasma. By far the most aesthetically pleasing tube I have when running, lots of plasma. These don't tend to output too much. 2-3mW max generally is a pretty high output tube. Though they're notably very visible as you'll see when you get to them. That's to be expected as its very close to the peak at 555nm. Just don't zap yourself with these open tubes, got myself twice yesterday messing with my 612nm REO.
Once you get the basics, feel free to look around for a 594, Sam is just about the only source for them..you could try searching for model numbers on fleebay, I do that to get some gems, but they're infrequent. These also don't output too much without tossing around a pretty penny. I don't want to talk about the price tag of my 594nm LYR. If you want to search fleebay for these, your keyword is LYR. Sometimes though it just takes an eye for finding what doesn't look normal. That just comes with looking at thousands of fleebay items and what they normally are/look like.
Next I'd put the oranges, 612 and 604nm. Good luck on the latter of the two. For 612nm, I'd recommend Sam again, or wait for the usualy biannual one to pop up on the forums, again, psu is everything. For these, search LOR. Again, you sometimes just find something odd when searching HeNe laser. It's a gamble though. These you WILL pay a pretty penny for, regardless. I paid $500 for my 2mW 612nm and that was before it was known to be ML. These are very hard to come by, not nearly as frequent as 633 or 543, even harder than 594. Though they ARE stunning
For 604nm....good luck. You're only get single line 604 out of a REO tunable, or a DIY tunable made from a 1B tube, though it's still hard to get. You're more likely to get this from an ML unit. Even then you're only getting it from a >$400 594 or 612nm. It does feel exclusive having it though. It's a special feeling. For the true wavelength hunter
Multilines are something to always check for. Just make sure you've got the perfect psu, then stick a diffraction grating infront of the output. Got nothing? Let it warm up a bit, who knows.
Lastly, infrared. Again. Good luck. I'm still looking
. You've got 1523nm and 3391nm. I'd say the 1523nm line is much more common. I let one slip on fleebay a while ago, it was in a mass HeNe lot and by the time I messages them about buying it separately, they already had. So good luck to that person! These don't always work either, so these are quite the journey really.
And that's all I've got! I don't know enough about argon to even try, that's Dave's game. Also didn't mention Raman or tunable lasers as they're still pretty new to me.
