As far as I'm aware, no one currently makes such a product. On the other hand, one could rather easily build such a thing with easy to get components and prebuilt modules if they were so inclined. Just running over the needed parts in my head with recent prices, and erring on the expensive side, you're looking at maybe $15 for a base station that connects to your Legacy or TMCC base, and perhaps $15-20 for each remote you want. Such a thing would provide a TMCC level of control over the engines with a simplistic remote similar to lion chief remotes, built in a small plastic project box. A dial for speed, whistle/bell buttons, uncoupler buttons perhaps, and whatever other features might be desired.
Of course the pricing mentioned just covers the parts. I'm unsure if if it would be worth someone's time to put it together or not considering the niche market for such a remote. Then again, I bet the materials cost could be dropped quite a bit if one took their time sourcing the parts and was going to make at least a dozen or two remotes.
JGL