The editorial alpina map is quite good but lacks topographic détails. I used the 2008 edition and there are quite a few errors. A better map at 1:25 000 is the Adrados editions which can be purchased in the shops in Potes, Cangas de Onis etc. I was last there 3 yrs ago and a local guide told me it was the best map for the Picos.
Wild camping is actually permitted from dusk to dawn above 1400m. As well as campsites there are also "zona de acampado" which are areas where camping is permitted that are not campsites. There is one near the Lagos de Covadonga, another near Cain that I know of. In addition there are quite a few refuges that are not guarded which can be used for free. Not sure of camping outside refuges as I have never seen tents outside them.
Leire must have stopped selling them. Intermarché does sell camping gaz but i doubt the screw top version. I'll have a look this week (in both shops), but normally in France they don't start stocking things like that until june. Regarding camping, I have mentioned it on another thread but you could camp for free (wild camp-ish) on the Baie de Txingudi. 10mins walk from the station, water tap and not far from public toilets. Fairly busy but every year there are festivals and people camp there with no hassle and it is right on the GR10