The only problem I see with basting brush bristles is the fact that they are just slim silicone flat ended rods, there is no tapering to a point like quills should.
They would still be ok if it doesn't bother you but it would me.
Also, the link that "Hunter-Hunted" provided is NOT for latex quills, it is for sculpy bend and bake quills for latex "masks" these quills are ok, they look great but sculpy turns brittle when it comes into contact with super glue, so If you have a bio or if you are wearing a costume with quills, they will be continually falling off and will need replacing every now and then.
All my quills have been made from latex, I have been using latex quills for a couple of years now, way before Termok lol.
The way I make them is fairly easy.
I found the it is best to mould them in small batches (5/6 at a time) take some toothpicks and give them a thin coat of milliput or something similar (epoxy putty) when cured, give them a sand so they taper nicly to a point, (toothpicks are not usually tapered) then, give them a coat of varnish (to prevent the exposed wood from going soggy during the moulding process making them inposible to remove from the finished mould) then, get a plastic cup ( the disposable kind) and place a small amount of plastasine or similare in the bottom, then push 5/6 shapped toothpicks into the plastasine until they are standing upright by themselves making sure they are ALL level with each other. then, fill the cup up with plaster leaving just the very points of the toothpicks exposed (this is to provide an airway for the latex when you pour it into the mould, if you dont leave a breath hole and your mould is closed then you will end up with an air bubble inside the mould and will not fill it up with latex) later, when the plaster is dry, tear the cup off the plaster, remove the plastacine and pull out the toothpicks, run your mould under water and drain quickly as you want it to have a wet surface when you fill it to prevent air bubbles, then fill it with coloured latex and as soon as the latex starts dripping from the holes in the bottom of the mould, you know that the latex has filled it completely and there is no trapped air inside, sqish some clay over the hole (not too much though as you dont want the clay going inside the hole, just cover it) then wait for it to dry......hey presto....latex quills.
Hope this helps......and i'll keep an eye out for tapered silicone quills
For those who are not bothered about the flat ends, would one of those spikey kids silicone toys be any cheaper? you know, from the 99p store, they are only..erm...99p.