I am new to fountain pens and have only just started to acquire some. I have started with desk pens to fill the pen holder from my great-grandfather. The pen I have is a cartridge type and I am wondering what adapeter, if any, would work. I have a waterman pen(new) and the refillable adapter for that pen will not work because it won't seal on the tube. I also tried to use a cross cartridge and same problem. I should state that We have little or no local sources for pens or ink here and I have to order everything thus my attempts to use what I had on hand.

Pendemonium sells converters. They're a great company to deal with!
http://pendemonium.com/

Just to give options (as I have also had good experience with Pendemonium and would happily recommend them)--

Swisher Pens is another company I can say the same of-- you'd probably do well to e-mail whoever you go with to consult about which converter is best for your model(s) of pen. The good news is Sheaffer hasn't changed their cartridge since they first came out, so it's pretty certain that one of the converters will suit.