United Kingdom company asking private label Shirts

Dear Sir/Madame,
I am enquiring about your production services, and deliveries to wholesaler/warehouses, on behalf of my student team from Lancaster University.
Our academic project is to 'create' a start-up business.
We are a shirt company called Pegasus Apparel that makes shirts to fit the irregular size dimensions of male, muscular athletes.
We aim to start with selling 10 shirt style variations, and these will have 12 possible sizing ranges.
This is due to size being classified by Sho