The only "widely available" ones are the Chinese Wico knock-offs, and those are 4-way bases.
It might be possible to hang a set of leaf switches on one of the other switchable joysticks (T-stik, Prodigy, J-stick, etc...), but I don't know what purpose it would serve.
The best way to get a 4/8-way switchable Wico is to build a restrictor plate for it.
Oscar used to sell them, and may be willing to give you dimensions on it, so you don't have to reinvent the wheel.