first off I am no expert know it all
BUT I don't think anyone makes a brush cutter that small for a skid steer, due to, most all skid steers are wider than 44-48 inches, and you would then be driving/running over all sorts of things with your tires
NOT knowing what model you have your or flow rates on your hydraulics
even recommending any brush cutter is rather impossible
as you have to match the flow rate to a cutter
BUT if your dead set on getting a SMALL brush cutter for a fll sized skid steer
I would say your only option or possible one, might be getting an adapter/conversion from full sized skid steer quick attach, and convert to a MINI skid steer,
and then look at brush cutters designed for mini skid steers
BUT heads up, most are not built to work on a full sized skid steer, in that, a modern full sized skid steer has way more power and can damage a mini skid steer implement due to having more power and weight in motion!
NOW< if you wanted other options, you can always get a walk behind brush cutter(like a DR make model)
ior one you can tow behind a lawn mower, or-if you add a hitch to your skid steer, use that to tow it?
they would have there own engine to power them
and in case you do find one for a skid steer, make sure you use a GOOD door on your machine, brush hogs and such throw a lot of debris in ALL directions, and why dedicated skid steers have heavy duty safety doors and side glass protection on them