Hair s
Dermmatch is better for beards - fill in gaps precisely and also cover greys if need be. Very useful product all round - Hair, beard, 'tash, sideburns or anywhere else you care to mention, or not!
Any chemist, supermarket etc - look under "Hairsprays
Any regular one from any supermarket or chemist - there's dozens of different brands - maybe find one with strong hold.
I use both - coat the scalp and surrounding areas with Dermmatch, when dry apply the fibres and pat them in place where needed. This will create a 2 in 1 effect for maximum concealment. You definitely have enough to work with!