I bought them from him direct. It was too long ago for me to remember how much I paid, his site says 29.50 GBP. He ships to the US.
From his site;

Delivery Overseas

All delivery costs quoted are for UK mainland only. For all other areas please contact us for a quote on postage costs. Please be aware that some items are bulky and/or heavy so can be very expensive for overseas deliveries.

https://jbfab.co.uk/product/extended-seat-brackets/

John McGee has these
https://sites.google.com/site/mcgeesminis/products

Jet motors has these 
https://jetmotorsmini.com/products/adjustable-seat-bracket

The Jet ones, looks like to me that you could mount them to the rear of the crossmember and bolt through them into the stock front brackets to get the same effect as the front/rear mounted ones. In fact it would be really easy to weld up a piece of bar stock with a rear mount to do exactly that.

I took a gander on their site and it didnt seem like they shipped to the US. Where did you order them from? Recall a price?

I wish i could just go to a JY and snag mini parts so i could butcher a pair and make my own??

I have them. They're very nicely made. They bolt to the original attachment at the front, I used 6mm rivnuts at the back. This picture on his Facebook page is my car. They won't get a wide seat back further than the other style as it will still hit the bins. The attachment across the cross member just feels much more secure.

Does Anybody run these or something similiar? They look nice.Are there any other company's that make them ?