Are you actually hiring for an in house developer, or for a consulatant to help you build your database to 13?
If it's the former, you might try posting to places like filemakerjobboard.com.
If it's the latter, elance might be a good place to start, or there's a myriad of consultants that would be willing to quote your project and help you.
Thanks again for your suggestion, however the site doesn't give sufficient freedom to post this, it seems to prefare more permenant posts.
which site? elance or the job board?
You might also try the UK consultants list to see if any shops can assist you in a consulting capacity:
And you get what you pay for (cheap is cheap)... But I never bid, just "rough estimate".
Go to any list ( here, FMI or filemakerjobboard or ???), but be sure to get references and check them out before choosing any developer.