Where can I exchange NANO for BTC

Where can I exchange NANO for BTC, some service or exchange avaible?

Since exchanges currently don't allow deposits/withdrawal using Nano due to the recent spamm attack the answer is, nowhere.

The fix is being tested on the main-net and exchanges are expected to open once everything works fine again. I can't guarantee when this is going to happen, my opinion is that a few days at the most are needed for everything to go back to normal.

ok and is there some source, that can I get notification on, that let me known that deposit/withdraw is possible now?

If you're okay with KYC — OKEx.

If the amount is not large, then wait 1-2 weeks and trading will reopen.