Hi everyone :)
Thankyou so much for replying.
I've managed to find some bucket teats that are a little longer and am waiting for them to come in the post.
The problem with the pull on teats or bottle teats were that they had a hole in the end, whereas the ones for the bucket had two little slits like this 'X'
I had been in touch with The National Foaling Bank and of course my vet has been here.
We did try a fostermare that had just lost her own foal but it didn't work out and there was no maternal instinct at all :(
She's strong and healthy so far and we did manage to feed her all of her mothers colostrum the first day.
Thankyou again for your help :)