Pet Services: Medical Center

My parents have moved into an assisted living apartment near the medical center. They have two cats (which are OK w/the apartment, 2 cats = 2 litter boxes) but have stopped cleaning their litter.

Can anyone recommend a pet service that can go out 2-3 times per week to sift and empty their cat litter? I don't live in town and don't make it in enough to help them with this.