Living in the UK, of the 3 I only get access to good (and bad) fish and chips. I used to live in the Boston area and fried clams or steamers were a particular thing my dad used to go nuts for. I loved them too and miss them dearly. I had no idea that HoJo's sold them. In fact I think I only remember going to a HoJo's once in my life
Mussels are a reasonable alternative to steamed clams and I've had those on a number of occasions in London. Not sure how available they are more broadly.
As much as I like mussels, they are NOT the same. (They are readily available in my area and moules marinere are something I do enjoy, especially in a nice pernod cream...) But New England fried belly clams have a taste that just can't (or more likely won't) be replicated elsewhere. Along with a good cheese steak but that's a whole 'nother thread ;)