Do you mean more an MCC than an MC? Only one I know of is Sarum bikers but that's a bit far for you in Bath. Google MCC along with Wiltshire/bath/etc I'm sure something will turn up.

If you mean an MC then there is one in Swindon, one in Andover and I think there may be one somewhere around Pewsey. I doubt they hand out online membership packs though so you probably want to find a public event of theirs or something and go introduce yourself.