the pop outs sell upto about £500. i have heard of people using windows from e30 beemers with a little modification.
the windows are readfily available if you look in the right places and have the cash to spend.
however the seals are more than obsolete, more like non existent. so then comes the fun of finding something else to fit...such as e30 beemer seals.
the mk3.5 conversion is popular and consists of wings, bonnet, bumper, panel and lights from a 3.5 soft top. Cars such as Tank Patels is a 3.5