Black light can be gotten in any electric supply house ..prob even a toy/hobbie store. Even ebay. I have one , but I don't use it as much as my Halogen detector..that way , I do not have to inject the dye.
Evap leaks are best spotted by sticking the detector up the drain after a long sit as the low side leaks faster when non use, as the low side has higher pressure then. Refrigerant is heavier than air , so it lays down at the drain connections ,if not disturbed. Sniffing up the drain tube after a long sit [even overnight]usually gets good results if there is a leak there.
A 30 pounder is nice to have b/c the last few weeks has seen a good price jump. Genetron is Honywells Trade name for refrigerants . If the one you have has the UV dye , it will say 134aUV on the bottle. If no dye , it will just say 134a. I guess Duponts Freon name caught on as it is common to hear Freon refered to as the refrigerant, no matter who made it .. you just don't hear someone say . "Hey, I think your aux. fan is not coming on cuz you are a little low on Genetron"...
You mentioned no oil feel in the liquid, so I assume it to be possible anti freeze from a pevious leak that may have just accululated in the bottom of the evap shroud and got washed out with the condensate that you now have from a working system.. specially as the drains are right on the sides of the tranny tunnel. Keep an eye on it and water drain is confirmation that you have a cold evaporator.. Good luck with the leak test