A quick Google for "midi to osc converter" shows a lot of people have had the same issue in various situations and some of the hits cover solutions that are on offer. These include free options.
I haven't time to review any of the options and, even if I did you should still carry out your own research but I am intrigued by the first result I got. ShowCockpit, it costs between €30 and .€299 depending on on the options you want and seems to be well documented. This is not a reccomendation but it interested me enough that I may give it a try myself even though I already use a TouchOSC thing I wrote which includes midi input and OSC output. In 24 years I've had one touring show come in that wanted midi control of the desk and it might be handy to have a solution on standby in case it happens again.
Looking at free options I found MidiMonster interesting. It is open source and appears to be free. It's a bit more complicated to set up but not too bad and there is documentation although it seems a bit sketchy. Again, you should do your own research - there could be better options.
When you get a solution that works you should give the forum a heads up as there may be others that need it.