inventory allocation to various customers

[3D-Cast]

Hi

I import products about every 3 to 4 months to stock up my shopify shop. I have a wholesale section and a retail section.

My wholesale customers like to buy per month and the retail is just when ever. How can I allocate stock of the same product to my wholesale customers and retail customers separately. I want this to ensure the retail wont over sell my wholesale allocation, but still allow my wholesale customers to by monthly from their total 3 or 4 month quota. My wholesale customers login in via a third party app to get the wholesale price.

I hope I've explained that ok 

Thanks

Luke