Don, I don't know what your price range is. The excellent (emphasis)
Sigma EX AF 70-200 f2.8 can be had for $500+ used, but you may need to
search for one for a while.
Keep in mind that at 210 mm., your SMC F 70-210 is very sharp wide open
-- if you can solve the focusing problem. I assume you don't use or have
autofocus.
There's always the option of going to f2.8 primes in 135 and 200 focal
lengths.