Happy new year Thomas,

If you're multihomed, getting an AS number from ARIN is trivial. Fill out the form, indicate the at least IPv4 /24 or IPv6 /48 you intend to announce via BGP, provide redacted billing statements from two ISPs and you're golden.

If you're not multihomed, buy a $20 virtual server from Vultr or a comparable cloud service, read about the BGP service they provide (BGP via two providers is what will make you multihomed), set up a VPN from there back to your site and then see multihomed above.

If you don't have at least a /24 or /48... why do you want an AS number? How would you use it?

Regards,

Bill Herrin