From experience,if your product is extremely unique and in demand, and will attract midro and upper class, try chandarania, they sometimes take stuff very easily, the manager has a look and places it on shelf on "consignment basis", OTHERWISE as a startup i would advise you to completely forget about Kenyan supermarkets as a launching pad for your business. That is for heavyweights with hundreds of millions to start off with. If you are small, the employees who can "help you" get your product on the shelf will ringa ringa until you can bribe them with a few hundred K or a milli, to get on the shelve, very nasty and thick fellows, then your stock has to "sleep" on their shelves, and to hire marketing people to get some movement for all the "malls" and "supermarkets" the best quote is kitu another mio, for a small timer sme like yourself.
At the end of of the day, many people have endured the above with a lot of hope, and still fallen flat, countless products, think of the milk and yourghat companies gone under, grain packing, food processing, hundreds don't make it, by far the majority. The supermarkets indeed serve a small portion of Kenyans, kiosks and kadogo and mama mboga serve the majority, that is where you want to succeed, start small think big!
Ras Kienyeji Man