This is one of the great debates in antiques and 1/2 our team naturally use more common spelling, whilst the other 1/2 use the technically correct version.
So which is right?
Let's refer the ever reliable Oxford English Dictionary:
2 able to be collected: a hire car, collectable on your arrival.
>noun (usu. collectibles) an item valued and sought by collectors.
Therefore collect-i-bles is technically correct, so going forward that is what we will try to use - however we're not pedantic enough to fire anyone if they slip up! We just love old stuff.