but we're required by law to do it.
I would have a chat with whomever told you that. I know for a fact you don't have to supply a VAT,
or a IRS number when you purchase WHMCS and they are a company based in the UK: UK Registered Company #6265962. Vat No. GB 927 7746 76
There is also Reseller-Club Mods which is a company outside of the USA that I have done business with as well and again there was no need for IRS numbers or VAT.
ResellerClub Mods (gIF)
NIF: 43281551J
C\Las Margaritas 39
35100 San Agustin
Las Palmas de Gran Canaria
España - Spain
Both of these companies are people I have done business with and both of them as you can see are outside of the USA.
All that said I don't know if the rules you are talking about are specific to your region, or not, but that is the experiences I have had dealing with people outside of the USA.