I know of no legal reason why Gold Chloride cannot be sold to any individual, even under the disgustingly restrictive legal regime now pertaining in the UK.
I have my suspicions, however. Any legally-available chemical can be sold to a company, I can get almost anything if I register myself as a Limited Company (plc or ltd), but I think the problem is the raw material cost/risk of default ratio. If you are selling huge amounts of chemicals, then a default (failure to pay up) is less problematic with a company which can be sued, compared with an individual who may do a charge-back on a credit card or via PayPal. I only got my chemical company to supply me with Gold Chloride because I wandered into their office with a smile on my face and 450 GBP in my hand, and plonked it down on the sales desk with a formal written order; and they know me personally, as I collect my DW in person. Even then, although I know that Gold Chloride is expensive, the absurdly small amount I received made it uneconomic to repeat the process, compared with electrolysis of pure gold wire. UK/EU pricing again. The size of the market in the USA makes many things much more economic across the pond.
Sadly, in the UK many companies won't do business with individuals in the Southern EU countries either, and state this on their websites. This is nothing to do with legal restrictions; I am also aware of police officers who try and "persuade" shops not to sell perfectly legal fixed-blade knives or blank-firing handguns in a particular seaside town on the South coast of England. There is no legal recourse in the UK if a shopkeeper or mail-order company succumbs to police pressure to withdraw sales to certain people. A well-known militaria shop was effectively "run out of town" near here, and had to move to a relatively remote part of Wales in order to continue his business; amusingly, he now has better sales as his new location is within easy driving distance of the premier Special Forces location in the UK. For another example, 15 vol H2O2 has no legal restrictions, but you can no longer buy it in bulk. This is an "agreement" between the manufacturers/wholesalers and the filth police, and few people have the backbone to resist. You have to be a known hairdresser to get 10% in most places, if you want a couple of gallons or more.