So, the rear tyre on my road bike has worn down so wear indicators getting hard to see so figure soon be time to change plus lots of little nicks in tyre so it's going to need changing soonish. Currently have Continental GPS 4000ii on front and rear wheels. Now, I'm quite happy with the 4000s but do Continental still make these? I'm in UK and doing quick google search it seems all stores online out of stock or is it that these tyres not made any more?
I know the GPS 5000 are the newish range but wondering if 4000 still made. If not, what's thought on new 5000 on rear but keeping still good 4000 on front? Probably not great idea but what about putting new 5000 on front and putting old but still good 4000 from front onto rear?
Now, if need be I'll just buy 2 brand new GPS 5000 tyres and stick them on job done but seems such a waste and enviromentally unsound to just bin a perfectly good front tyre.

Thoughts?