Ryan,
You KNOW that the Sunn never shines in the UK!
Seriously, Sunn amps divide into two generations, pre-Fender and Fender. This forum is mostly dedicated to dinosaurs, like me, who have original Sunn amps from the Pacific Northwest. I don't know if these were ever sold in UK or even if 220V models even exist.
Fender later acquired the company and reissued two Sunn amps, the Model T for guitar and a bass amp. These are modern amps, have nothing in common with the old Sunns, but are generally well though of. Fender has since discontinued the line and most factory new Sunns have been cleared out. You might check eBay and see what you get. Again, I don't know if they ever built an export model. Check with a Fender dealer and see if they have one they would like to unload. If so, you might get a great amp at a great price.
Or, wait a few years. The Sunn will rise again.