I got a set from Gemm4x4, there were different varieties depending on the starter/engine combo.
easy to replace, the starter should be quite easy to remove (2 bolts?, possibly 3... can't remember), which will allow you to fit new brushes more easily.
the symptoms i had for worn brushes were:-
1) sometime just clicking but no turney
2) clicking and very slow turnover with a strange clackety sound.
cheers
Stephen