This is old as hell but I do recommend a web-based solution.
This code runs in your browser and does never send your data anywhere else. Everything remains local on your machine.
How do I know? I built it specifically for that purpose.
You might want to give a go to following two opensource projects which really are alternatives to MS Access:
I have used both of these for bigger clients and to their complete satisfaction.
gratis support from me
extensive performance tests and sparse unit tests
almost perfectly mimicking the interface of std::unordered_map
open addressing using linear probing with pseudorandom ordering (similar to Robin-Hood hashing)
I had a similar problem, I need a hash table that was not just faster but also more memory efficient, ...