That is a 10-turn trim pot. The photo shows the style with screwdriver adjust.
Nobody makes after-market knobs for that style pot because there is not enough shaft to connect to.
There are OTHER styles of trim pots with knobs. Here is a style with an extended, knurled shaft that can be turned with your fingers (or with a screwdriver).

And here is a single-turn pot with built-in knob.
