Been using some presta tube recently and lost one of my Shraeder to presta rim conveter inserts – Trying to find an online shop that does them?

Not necessary. I wouldn't bother if I were you.

(I'd just keep using Schrader valves, because they're stronger, but that's not the question…)

You don't think that the valve will bulge throught he hole or rub against the sides of the valve hole?

did find some though with the power of google 🙂

http://www.ukbikestore.co.uk/product/59/rt20/mavic-schreader-presta-rim-hole-adapters-10-pack.html

Just a question, but why not stick with Scrader valves, then there's no problem…..?

Got a load of presta's for another wheelset so just wanted to use those instead of buying some new Shraeder valves 🙂 The only reason really 🙂