A Chairde,

My local club run a lotto and have the name in Irish as Cairde Seamróga Ros Liath (Friends of Roslea Shamrocks). I don't think this is correct. My attempt would be Cairde na Seamróg Ros Liath. Just wanted to check the correct translation of this.

GRMA,
Seán

Ros Liath is a proper name. It is definite. So there can't be the article na.
Ros Liath is in genitive case, (shamrocks of Rosslea). So, seamróga can't be in the form of genitive case.

I'd say:
Cairde Sheamróga Ros Liath

Go raibh maith agat a Labhrás.