Refills for the majority of writing instruments purchased from JS Pens are available from any reputable stationer and High Street shops such as W H Smith or Rymans.
Fountain Pens: These usually come with both ink reservoir and cartridge. Any reputable ink such as Parker's or Quink should work well in your fountain pen reservoir. Any standard European Ink cartridge should work well in your Fountain Pen.
Rollerball: As there are a number of different Rollerball refills on the market I suggest you shop with your empty refill to hand.
Twist Pen: These take either a Cross style refill or a Parker style refill. Both are easily found in the High Street.
Pencil: These take a standard lead refill at either 0.5mm or 0.7mm.