You may try to ask about Kulma here - http://www.tajiktour.tajnet.com/
but now this site is down, I hope temporarily. But in any case this is unreliable - by the way, Torugart pass officially is also open only to Chinese and Tajik, but really it works for all nationalities.
The road from Sary-Tash to Kashi (Kashgar) is the most reliable, but not most interesting.
About road through Kyrgistan. Yes, there is a good road from Bishkek to Isik-Kul, but there is a way more interesting - this is a new mountain road from Almati to Isik-Kul lake. I was where in 2002, it's great! But this road is extremely difficult, there are 2 pass, one of them is terrible for cyclist.