Here is a suggestion. get some t81 wheels and get a 5/16 hub and tap it for 3/8 ( might need to double check that but the chart i looked at said that was the size of hole you needed to tap 3/8 tread into) and us t81 wheels. The big downside is that i cannot find them being sold in the UK so banebots is the only place to get them so cost can be a issue. Also if you don't have a tap and die set or not able to get someone to do it for you locally that is another cost.