Assuming you are looking for an experienced Administrator, and not "merely" someone smart who you can train:
I have no good sources other than the one you are using right now (BenefitsLink) - which is excellent. Unless you hit someone who is looking to relocate ALREADY, the general feedback that I've seen is that normal Admin positions frequently don't pay enough to entice people to relocate. If you are offering relocation expenses, that might help a lot. (If you move your business to Maui, you might get a lot more applicants. 😎)
I've also heard, anecdotally, that many of the larger companies, while they have some very good people, often compartmentalize - so someone may be very good at Nondiscrimination testing, but can't interpret a document or do a 5500 form or a VCP filing. So getting the trained person you want, at a price you want to pay, can be very challenging. Subject of course to local conditions/labor supply.
It also seems to me that some of the younger generation has some unrealistic demands on salaries/benefits. (When I started, plans were pretty simple - we did them with a hammer and chisel on stone tablets, and benefit formulas were 1 goat per year of service up to 25...)
If you are willing to train, then job fairs at local colleges can work. At my prior employer, (a much larger company) we picked up a couple of excellent people. Problem there is that if you are a small TPA, there isn't generally a lot of room for advancement, so the 20-somethings move on.
Sorry I can't provide more helpful suggestions. Good luck!