captcha option for custom registration page

I've got a custom registration page (built off wp-signup.php) located in my theme folder. Have tried four or five captcha plugins and none seem to be able to 'find' the page. Have posted with several of the plugin developers and haven't gotten a response, so thought I'd see if anyone here knows what the best option is.

Install my own captcha code from a non-wordpress plugin?

Getting a few spam registrations a day and would love to get something in place before the flood starts.