Okay, I'm not terribly experienced with all of this, but I will give it a try

My understanding, after hours of research, is that the preferred method of dying prefolds is vat dying, i.e. using a pot or tub of some sort to soak the prefolds in the dye solution. This seems to be what fiber-reactive dyes need. You can dye prefolds in a washer, using RIT dyes, but you will likely be dissapointed, as RIT dyes apparently wash out of all-cotton fabric. Fiber-reactive dyes are the best for all-cotton fabrics. Dharma Trading is the more popular source for fiber-reactive dyes, but you may be able to find Dylon Cold dyes or Rainbow Rock dyes locally. I know my Michaels carries Rainbow Rock dyes, in solid shades as well as tie-dye kits. Joannes also carries Rainbow Rock in tie-dye kits, and so does Walmart.
Hopefully, I was somewhat helpful to you
