The frames are pretty standard for the LiTP posters, 40x50cm, they are sold everywhere. The posters are A3, so I got the mounts cut to order. The 75th anniversary poster is A2 so used a standard 50x70cm frame, again with a custom mount. You can get frames A3 and A2 size, but I think a mount makes things look better, and it gives you a wider variety of frames to choose from. Custom mounts are way cheaper than custom frames! The four frames and cut mounts cost around £70 and I used Elliotts in Lincoln.
Thank you for your lovely comments.