If you need something to hold you over until you find a supplier, Rexall (drug store) has sheets of 10 P-Stamps for 10 percent off until Feb 1st. They run that sale periodically. They have a limit of 4 sheets (40 stamps). If you go with a friend or family member, you should be able to circumvent the limit.
Rexall's app also has offers where if you spend a certain amount, you get a rebate in the form of points useable in store. I am unsure if Stamps are excluded from this. As an example, they will might have spend $50 get $10 back in points.
I understand that if you were dealing with a supplier and using smaller denominations, you were likely getting a steeper discount than 10 percent.
If you google discount postage, there are a few suppliers who come up near the top of the results. I would reach out to each one and see which (if any) are a fit for your needs.
