You know that would be a cool idea, there aren't many conditioner bars marketed for afro curly hair, HOWEVER, for cost reasons I can see why they havent. Making a conditioner bar is expensive and I would think a lot of companies would be afraid of preservation issues. A conditioner bar is basically a very very concentrated chunk of conditioner. Your average indie conditioner contains about 5-10% btms. That ranges from leave in condtiioners to deep conditioners. A conditioner BAR can be up to 60% btms by itself easily. They could I suppose use stearic acid to keep the bar hard instead of having to use such a large percentage of conditioning waxes but that would just make the product draggy. Conditioner bars are also constantly in water. Yes, a consumer could break a piece off an use that on their hair instead, BUT what if they dont use all of it up in one wash? Chances are theyll try to reuse it (bc who really wants to throw money down the drain,,,,no pun intended) anyway and voila youre introducing possible bacteria, mold issues. Now I know you can use a preservative for a condtiioner bar, but as a business...keeping in mind the fact that the entire product would be drenched in water...I would be afraid to sell a product like that.
Then, and from a businesses point of view, a conditioner bar lasts.....for ever. Seriously. You can get at best maybe 10 uses out of a bottled 8 oz conditioner....with a conditioner BAR, because its so concentrated, you can get easily double that amount. So a customer could get more usage out of it (thus not having to rebuy for a longer period of time), the business would be using a higher concentration of ingredients (expense), and IMHO most people are accustomed to conditioner bars being cheap even though they use a higher concentration of ingredients so the amount they could sell the product for would probably be limited (anywhere from $5-$14 maybe without people calling it overpriced, even though....again...it will last longer and cost the business more to produce, with more risks on their end).
Why don't you make your own conditioner bar? Theyre fun to make, and its easy to customize them without having to deal with emulsifying issues. I make a lot for myself to the point where I rarely use botttled conditioner. I have deep conditioner bars, co wash conditioner bars, and even leave in conditioner bars. You should get a bit of btms and cetyl alcohol and give it a go.
Here's a simple recipe that you can use that I tried when I first started making mine. Theres no exact science and you can use an ice cube mold or any other mold you have lying around.
10% cetyl alcohol
10% shea butter
20% oil of choice
Heat it all up together, and let is solidify in a mold. You can add fragrance if you want as well. Since I make these myself...a cool trick later if I need a moisture spray it Ill cut a chunk of the conditioner bar off and add it to some distilled water and shake the bottle well, and it quickly makes a detangling and moisturising curl refresher. You would need a preservative for this really but I suppose if you are okay with making the spray in small amounts it would be okay.
Also you could try lactic acid with regard to ph if you are concerned about that.