http://mx5oc.co.uk/forum/forums/t/353.aspx I posted this one
http://staging.mx5oc.co.uk/forum/forums/p/193/354.aspx#354 Fergy posted this one, it comes from the staging forum ??? 
Hello All, At the top of the suspension on my mk2 there is a rubber doughnut sandwiched between the topmount and washer / fixing nut. I thought of replacing them because they are looking worn and have cracked around the edge. Does anyone know where to get them from and are ploy upgrades available. http://i476.photobucket.com/albums/rr125/checkmate_toby/P1010020.jpg
Try Mazda; the whole bush assembly for the top mount is only £10 or so.
I think poly replacements are available from Superflex,
Superpro or Polyflex. Google polyeurathane bushes, might find you the
right company.
An upate for the Forum…
I tried several companies for Poly versions but I could not find any for my mk2. So I bought a set of 4 OEM parts from MAZDA. All parts were in stock.
MNC1028775 Upper Bushing £1.66 ea
MNC1028776 Lower Bushing £1.66 ea
MNC1028012B Spring Seat (Top) £9.35 ea