There are not too many avenues to find a Rukiga speaking mentor outside of Uganda. It is not a widely spoken language in the first place with maybe around 6-7 million speakers in contemporary times. That said, there are a few suggestions that I provide that might be possible places to find possible mentors or conversation partners.
Personal or Professional Networks
If you are interested in learning particularly Rukiga, then it might be the case that you may have connections to Uganda in some manner or fashion. Thus, you might want to connect to your personal or professional networks to see if you have anyone who would be interested. I think in general speakers of Rukiga would be happy to teach someone using WhatsApp or similar programs, particularly if the work is compensated in some fashion.
The African Studies Program at the UW or related programs in other Universities.
While more programs will likely have Luganda, if they have any Ugandan language, these sorts of program can be good resources to connect with possible mentors. You might be surprised what connections these programs have based on their alumni network, project contacts, or professional connections. It is at least worth a try!
This group or related groups could be another connection. Again I do not meet too many Bakiga in the US, but there are some, and, various African associations might be a place to start to make connections. In as similar to the types of university program mentioned above, it is at least worth a try!
A fairly well known language centre in Uganda; CLC has skilled teachers and knows what they are about in teaching Ugandan languages. I believe they are willing to do Zoom/Skype/WhatsApp tutoring calls, though it might cost a bit more. I would recommend connecting with them if you are interested in learning Rukiga and online learning is viable for you.