might depend on what dizzy you have could be 1 0f 3 fitted [?]I Do have a boxed set probably with part no on if thats any help [?]Try speedy spares.(still need to know what dizzy you have)should have an oil filter with part no too if you get stuck
Or try your local motor factors. You still need to know the dizzy type, one was the same as a Mini. The last oil filter I bought (ages ago) was a Champion C102.