Hi there...where about are you?
Our society does have lotty shop. We buy in bulk from local(ish) horticultural suppliers.
We try to buy ours in two biggish orders so we can get bulk discount and keep our prices down. Majority of the fertilizers are bought in sacks and the measured and divided into smaller amounts that are easier and more convenient for buyers.
We print our price list yearly for all members and these are sent together with AGM invites...otherwise price list is shown in shop.
With many if wholesale companies you just have to ring and ask their catalogue..and then ring again to negotiate the price for you..many of them are quite willing to tailor the prices depending how much you can spend in one go.
It is quite a job to get it all started but once you have your shop up and running its not that bad after that.
One of the companies we use is LBS Horticultural suppliers..its not the cheapest..but some stuff we get from them and it all comes down to negotiation..

LBS is nation wide company, once we know where about you are located..perharps somebody here will be able to help more with more local supplier.