Cordial drinks aren't as much of a thing in the US anyway.
Ribena's just Ribena. It's mixed with water almost exclusively, lemonade at a push, but blackcurrant cordial would be used for snakebites or rum+Guinness. Surely I'm not alone on this?
Of the actual snake variety, or are you meaning some kind of drink?
One can have a 'snakebite and black' adding a dash of black currant, also a 'black nasty' being a 'snakebite, pernod and black currant'.
There are alternative blackcurrant cordials for diluting which are much cheaper and taste good. I think every British supermarket has their own brand one.