How can I find someone to come and regularly assess my dad to determine if he needs additional care?
Absolutely. It sounds like you're describing a geriatric care manager, who acts as a kind of chief elder care organizer, helping connect the dots for their clients. You can find them on-line or in an old-fashioned paper telephone book. The Eldercare Locator is also a great source for finding geriatric care managers. You can also get referrals from local senior centers or your dad's medical staff.
A care manager may be a higher level of service than you need. You may need a home caregiver (versus manager), who can be hired through an agency or independently. The Eldercare Locator can also help you find home caregivers, as can geriatric care managers.
It sounds like you're making a wise move to get occasional help, as well as to help you keep track of your dad's needs.
In our area Hospice has been a real help as far as someone coming to sit with my husband and also for equipment that we need.