I think he's referring to drawing from an ampule, as that's how Sustanon is packaged.
Since there is no worry of damaging a rubber stopper with this medication, needle gauge doesn't really matter. But I don't think there are too many manufacturers producing filter needles in a wide variety of sizes.
I think BD only makes filter needles in 18g and 19g.
OP see if you can find some filter straws in your area. Same idea as the needle, just a plastic straw instead.
Or if that fails, you may have to order off the internet.