I have a 7230 and my employer does not support BES. I am interested in using astrasynch to get my emails. All my other apps work and synch fine.

And yes, I know this is an old handset. It suits 90% of my needs OK.

astrasync required OS 4.2 and higher but as far as I can tell OS 4.2 is not available for 7230. Is there a way around this?

AstraSync does not work with OS version 4.1 or earlier. The 7230 never got past 4.0 so no, you cannot use AstraSync with this model.