I've also been hit by the Royal Mail hack. My trials stuff was posted on the 9th Jan, still not left the UK yet....
In the US, try HVC Cycle. I ordered from them recently and i needed the parts delivered fast as my wife was flying into the US for only a few days (i'm in Canada) I emailed them after my order was placed and they responded promptly and fast tracked my order. Arrived all on time. So thumbs up for those guys.
I did order some parts from Sierra Motorcycle Supply (a Beta dealer). Total waste of time, they didn't have the parts in-stock (website didn't say anything), still took my money and i ended up cancelling my order for a refund. I had chase them for an order update as well. I'll not use them again.
For the UK suppliers,, there's a ton of them, it's just finding the one that has all the parts you want and has reasonable shipping to the US.