Welcome, I was going to point out the back stamp, but it looks like you've already found out about it.
Those are good looking cards. Since you pointed out that shipping across the pond is a difficulty, look into the COMC mailbox option. That allows you to send cards to an account in the US, where they process them and put them in your holdings. Then you can, at your timeline, have them packaged and mailed to you in the UK. There are other companies like "ShipMyCards" that do the same thing.
https://blog.comc.com/mailbox-service/
COMC also has plenty of T206s for sale, but the pricing there is very hit or miss since there's about 20,000 different card sellers using that site. Anything fairly priced seems to get snapped up quickly. But compared to tracked shipping internationally, it might be an option for you.