Just wanted to throw an idea or two at you, just incase it helps out.
I wanted to buy some very rare and not available inserts for Star Trek Next Gen (large 3 x green kidney inserts) and no-one anywhere in the world had them advertised anywhere for the last 3 years. I contacted Wayne Gillard in melbourne and he had a box of them, and was happy to sell me some (and Beaky) so we got the inserts we wanted.
At that time, Wayne had alot of different inserts for various machines that not all were advertised.
So check with Wayne in Australia, or check with Planetary Pinball in the USA just incase they have some inserts that may suit that they just havent got advertised.
Also, when I was cross referencing the inserts that are on my Gilligands Playfield, I found that the same inserts are used on other machines etc, so its a good idea to look up many pinball titles and see what parts they have listed, because sometimes you accidentally come accross the same inserts u are looking for, but they are showing in stock under a different titles stock listings. (check many Williams listings for example just in case u see them). The advice I have thrown in is a long shot, but sometimes long shots pay great dividends/results.