Chuck it up on the B/S/T. When you want one again, buy another one - preferably again on the B/S/T. A similar approach to Gumtree works best for most things in life. Reduces clutter and storage costs... and makes your house feel bigger. Avoids just finding things at the back of the cupboard after 20 years when you move house and then wondering why you ever kept them in the first place.
It means good brushes get used for their intended purpose rather than stored until the knot falls out and it's shedding clumps at a time...
Doesn't work for things of sentimental value of course but I try to limit myself to just 1-2 things like that in my life. Gotta keep looking forwards...