We do not sell ink, nor do we sell refill cartridges (except, occasionally, obsolete specimens of collector interest, most of which are no longer functional). Since we specialize in vintage pens, the only fountain pens we normally offer for sale that use modern plastic ink cartridges are Parkers and Watermans; in both cases, cartridges and converters are still being made and are readily available, although the supply of older Waterman cartridges is getting tight. Regarding refills for other brands of relatively recent manufacture, we regretfully plead ignorance: you are best advised to consult a stationer or new pen dealer.
We are also unable to provide much information on refills for older ballpoint pens. Modern Parker refills will fit all older Parker ballpoints, but many other brands will require either experimentation with currently-made refills or custom-made adaptors that may not be commercially available. Adaptors will generally always be necessary for first-generation ballpoints of the 1940s, such as the Reynolds, Eversharp CA, Biro, and Sheaffer Skywriter.
For further information on both refills and ink, look under Basics in our FAQ pages -- where you will also find information on finding lead and erasers for older pencils.