The simplest way to find them is check the sites of the knife suppliers.
USA Knifemakers, Jantz, TKS, Knifekits, K&G, etc.
For threaded standoffs to use as the inserts, I have found two types that are cheap and work well. Both will press in an approx. 1/4" hole. A standard or homemade counterbore will make the inside and outside recesses in the scales for a perfect fit. They can be found in any thread from M-2 to 10-32. I find 6-32 and 8-32 work well for take down or changeable handle knives.
The first is the phenolic standoff. It is easy to cut and sand top length, and will easily press in a tang hole. A dot of CA will hold them nicely snug. They are surprisingly robust. They can also be easily replaced. This isn't necessarily the exact ones you want ( 6-32 bolts), but they come in most all size thread:
http://www.ebay.com/itm/WALDOM-6037...936181?hash=item2a68075035:g:~2sAAOSw1DtXEjOo
This is the other type, also easy to be pressed in, an can be soldered in place if desired. Again, this is a sample photo ( 6-32 thread) and not necessarily the exact one you want:
http://www.ebay.com/itm/2209-KEYSTO...103659?hash=item56871e656b:g:4~UAAOSw-YBXGFvO
Depending on the size knife, #6 and #8 torx screws work well. Head shape can be your choice, but I like the truss head, flat head, and pan head shapes. Here is a sample of one that works well on knife handle scales:
http://www.knifekits.com/vcom/product_info.php?cPath=60_81_233&products_id=7002
TIP:
Make a hardened steel drilling jig up with the hole spacing's you will normally use. Use it to drill the holes in the scales and tangs. It should be for the clearance hole size of the screws you use. The tang hole then can be re-drilled for the spacers, and the scales can be counterbored for the screws and the spacers.This will assure the spacing is the same and that handle scales will fit the knife perfectly.
TIP #2:
There is a temptation to make the holes and seats in the scales too exact. The clearance hole should be a tad oversize, and the counterbore seat hole for the standoff and the screw also a tad oversize. (The hole through the metal tang is the only exact fit hole.) About 10% extra is a good amount to shoot for, but you may need even more. That sounds like a lot, but is very little in these small sizes. You want some "slop". On the #8 torx screws shown in the example, 10% oversize in the seat hole is an extra three one-hundredths of an inch. This allows the screws and spacers to all go in and seat right. There are too many ways that something will be a few hundredths off here and there for four or six screws to all seat perfect without some wiggle room.
I am sure some of the machinists are aghast at this huge overage, but they have the skill and equipment to get closer tolerances ... ands still have problems. The average knifemaker with a home shop will be lucky to get everything to fit with only 10% slop.
