Check ebay or local craigslist. I picked up 50 freshly molted adult females locally off craigslist for $40 and he threw in like 10 males as well even though I didn't need them. Can also check here or http://www.faunaclassifieds.com/.
Alright so I ordered some off of ebay and I have the tub all set up. It is a 18 gallon sterilite tub and I bought a 10-20 gallon under tank heater the kind that stick on and it is hardly raising the temp at all. The temp in the room is 70 and the temp probe is reading 75 and that is with the probe on the bottom of the tub right over the heat pad. I have a 150 watt ceramic heat emitter laying around and a extra dimmer could i use this and place it above the tub where the screen is? I need to get something figured out before the roaches get here next week.
I too had problems trying to heat a Sterilite tub with a reptile heat pad. I ended up getting a 45 gallon Rubbermaid Roughneck tote and the heating pad heats it np. Its a 30-40 gallon Zoo Med one that I use a lamp dimmer from Home Depot and turn it down to lowest setting and I get around 100 degrees on the floor of the bin. Can use a smaller one but I had the big heat pad laying around. Weird thing is the feeder bin is the 18 gallon Sterilite now and I have it sitting on top of my boa cage which has a solid top and uses a Pro-Product radiant heat panel and that seems to heat the bottom of the bin to mid 80s np. Anyways, you could use a CHE to heat the roach bin. I tried it with a 250 watt CHE I had laying around with a 300 watt max lamp dimmer and it mad the CHE hum like crazy so I quit that. Might work better with the 150 watt since you aren't trying to restrict so much of the power. At the moment for my breeder bin, like I said, I use the 45 gallon Rubbermaid roughneck tote with a strip of packing tape around the bin 1-2 from the top cause the little ones can climb the sides of that bin. Then I use 30-40 gallon Zoo med reptile heat pad with a Home Depot 300 watt lamp dimmer turned all the way down to lowest setting and then a 25 watt red bulb in a dome on top. that combo heats it fine and I got babies all over the place. The red light doesn't really give off much heat but it does allow me to see inside there without bugging the roaches since I got the top on the bin and have a 24x9 inch rectangular hole cut in the center of the top so I can reach in and give the roaches food and water.