What else besides a retention nco could I do to find a new reserve unit ?

You’ll need to contact USARC Human Resources.

If I understand your situation correctly:
*You were assigned to a reserve unit in PR but live in KY.
*You have not reported to the PR unit but you have emailed them with no responses.
*There is a local reserve unit retention NCO that has attempted to help you but you have not heard from him/her for a period of time.

I was in a loosely similar boat when I was working for NATO as a civilian and was pulled out of the IRR and assigned a unit in PA. I was definitely not going to be making a trek across the ocean once a month for unit assemblies. I ended up calling my branch manager. Unfortunately as enlisted you do not have a branch manager. I am sure that there is some sort of a personnel management office at USARC you could speak with. I would reach out to your local retention NCO contact though first as to not burn any bridges. He/she very well might be talking to the same USARC people you would be calling and waiting on them to get back with him/her.

In addition to what Major Cummings said, log on to the ARCD website, go under tools, and then vacancy locator. Fill in your MOS, grade and state and it will show you any vacancies. It will show you the unit, address, UIC, etc. This can prove helpful when you talk to your local retention NCO or chain of command as not only will it show you have done your due diligence, but that it's one less thing for them to search for and take up time.