Golden Week is less of an issue nowadays. Your exposure is fairly limited if you are only flying into Chengdu directly to go on a guided tour. Just plan early.
I found an English link:
https://www.trip.com/things-to-do/detail/17150021
Many more options if you access Chinese forums and sites. I did not engage a tour agent, but hitched onto a self-help travel group through a Chinese traveller forum. Basically a group was formed with a specific itinerary in mind, and everybody chartered a mini-bus charter for the itinerary.
Now it is entirely possible to do the whole thing without joining a tour group.
https://onthewayaround.com/yading-nature-reserve/#Getting_to_the_Yading_Nature_Reserve
There are coach services from Chengdu that will take you as far as Litang, Daocheng, Kangding and even Yading itself.
https://www.chinabusguide.com/chengdu-to-litang.html