Mine are pretty rubbish as well, the rear wiper judders bad. Keep meaning to replace them then the sun comes out and it goes on the back burner ...till the next rain and so the cycle continues lol.
I had a look online a while back for reasonably priced replacements but I was surprised at just how many blades there were perporting to fit the Mk3 that obviously didnt, even entering the reg number threw up wrong uns'. I did go out and measure them in the end, rear was 330mm, drivers 650mm, passengers 400mm - or in old money R_13", D_26" and P_16".....I think, dont quote me
Best get my finger out with the onset of Autumn, anyone thats bought them reasonably priced online feel free to post a link