I have located a source of a female to female "Luer" lock fitting that will allow you to connect 2 syringes nose to nose. This lets you draw the exact amounts of the colors into individual syringes and inject them into another syringe for mixing by pressing the plungers back and forth. I acquired my fittings from Value Plastics, Inc at www.valueplastics.com. You may wish to have your club or modelling group pool a purchase in order to meet any minimum quantity requirements.
Model FFLLC or FTLC made of nylon material which will handle most solvents or paints. Value lists nylon as compatible with Alcohol, Acetone, Ethylene Glycol, Isopropanol, Methyl Ethyl Ketone and Methanol.
Does anyone else have sources for the bottle caps?