Sorry I realise that you don't have Spotify in the US. There were actually 6075 tracks in the 'Celtic' genre and just under 43000 in the 'Folk' genre. Perhaps you know someone in the UK who you could join through and purchase a Premium version where I think you could use it in other countries.

A free user can use it outside the country for 14 days but no longer

I can't even use the free version here in the US.

A bit OT, maybe, but this illustrates a big reason why so many people steal music.   Because the powers-that-be make it so damned hard to buy it legitimately!    I'm a Rhapsody subscriber and it's the same with them when we travel outside the US - in most places we're cut off.    I don't even know who's doing it.   It can't be the record labels because almost all these bands are independents!