Dear Daylily:
I have no clue where you live, so I can't recommend specific institution 'food brokers' in your area, who may also sell single items to consumers. In eastern MA we have Cirelli's, Perkins, and a few other places that either carry this stuff in their 'retail' store(s), or will special order it for you.
Have you contacted the manufacturer to find out who buys their 'institutional' (aka 'bulk') products in your area? That would be my first move. You can bet that any 'institutional' (commercial) kitchen (kosher caterers, assisted living, nursing homes, etc.) aren't buying cases of 3 oz. boxes! Their contact information is listed below.
I just asked 'Mr. Miserly' (who is in the closeout business and also used to be in the used commercial food preparation equipment business) if he knew the size of institutional gelatin packages, and he didn't, but he said that cake mix comes in 5 lb. bags, and I'll bet that gelatin is probably similar. So, if you can use 5 lbs. (It takes quite a while to 'go bad' - we have some that 'won't gel' any more, but it's been around for 'quite a while' and I think it spent too much time in the garage, also), then that would probably be your best bet.
Vip Foods, Inc., 1080 Wyckoff Ave, Ridgewood, N.Y. 11385
Phone: (718) 821-5330, Fax: (718) 497-7110
Consumer Hotline: 1-800-83-KOJEL
For more information see their website at: http://www.vipfoodsinc.com/institutional.html.
Happy hunting!
Miserly Maxine