In Australia we have a number of manufacturers making tow hitches.
Classic Industries ,who also make a range of trailers, are probably the largest maker in AUS and make tow hitches for a very wide range of bikes. They have them
on the shelf and you will generally have it (in AUS) within three working days.
I have only had a Classic tow hitch for the Honda CB1300.
Other manufacturers in AUS (that I've found) will only custom make your hitch, this required a trip interstate or to a remote rural area, overnight stay - too much mucking around for me.
For the ST1300, I purchased one from an
OzSTOC member (it was on an ST13 that he purchased second hand). My ST13 hitch is
FAR SUPERIOR to the Classic hitch, much sturdier and heavier duty componentry. The previous owner said it was a US made hitch, I contacted the manufacturer for some information, but didn't get a response.
Some
eagle eyed ST-Owners member may have an idea.