Facebook Marketplace is where I found mine - a 6' fridge. Drilled the holes and put a piece of aluminium tube through it - all came in at £60. Holds 2 roe or 1 fallow. Wouldn't manage anything bigger though.
Keep an eye out at the back of service stations, convenience stores etc. They're always doing refits and upgrades, and the fridges they take out will be stood outside somewhere awaiting collection for disposal, which will cost them. They'll be glad of your offer to take it away FOC. Keep looking, and eventually you'll spot one, guaranteed.
I looked at the game fridges online (pricey!), but they suggest what size can hold what etc, anyways I sourced they're internal dimensions for the what I need (broadly two roe or one fallow), then bought an old catering Fridge with near identical internal measurements of ebay. Final bit being I put the shelf rails to highest and built a small frame to hang from, works for me