You can mix glitter dust, very fine glitters or colour pigments with clear gel to make your own colour/glitter gels.
I've used MAC powders, mineral eyeshadows & very fine glitters, the glitters can be picked up from any art & craft place or are quite cheap on ebay.
It will be trial and error to get the shade of colour you want and the less additives there are in the pigments you choose the less product you will need to add to your gel.
If you get nice strong pigments then you need only a tiny amount if your using cheaper products (old eyeshadow pallettes or cheap eyeshadows) then you may need to add a bit more or the colour may not look the same as the shadow does in the palette/pot.