I would also suggest giving the spammers more intense work to do. Like a pdf form for new suppliers that they have to download, fill out, sign, scan back in, and return. Or maybe submit to a form page with a horribly difficult captcha.
'[country] rules mean we need you fill out the attached pdf. Please complete and upload to [... IP logging website]'
EDIT: Or even just the PDF, really, I can host it on the server.
Make it count how many times they've attempted. Every-time clear random fields and randomise fields to make auto-filling neigh-on impossible.
edit Also re-order the form locations, placeholders so it's nearly impossible to script automation for the page!