There seem to be several good sources of pin loom needles. If you know about other sources, please let me know and I will list them here.
Lacis lists a Weave-it Needle, "A 6" straight shaft needle with yarn eye and blunt end specifically designed for the popular weaving boards." These appears to be the same as the needles that were originally packaged with the loom. It is interesting to note that the price of these needles has dropped. When I checked on them several years ago, the price was around $7.00 each. More recently I saw it priced at around $3.00. But don't count on my report, the prices may change regularly.
The newest resource for 6" and 4" needles has come about courtesy of the Zoom Loom. It appears that some Schact distributors also have Zoom Loom replacement needles available.

I also have to recommend the 5" Susan Bates Weaving Needle. This needle does not work well with the pin looms, it is a little too thick and short. However, it works great for joining squares and other weaving tasks. It is available at a variety of craft stores and the cost is low. Considering how precious the 6" weaving needles can be, this needle can substitute for all the other uses where a good yarn needle is needed. It has a nice rounded point and a very large eye.

An update: a friend pointed out that there are 4" doll needles that, with a little work, can serve as a weaving needle for any of the 2" wide looms. She noted seeing 4" needles at Hobby Lobby-- I think they are available at any doll related or large craft store. The needle needs to have its point rounded off. I find the doll needles to be a little too thin and therefor prone to bend. But the doll needles do offer another weaving option. MS
2nd update on 4" needles: (Actually 3.75" needles that work really well for 2" wide looms.) I recently purchased a package of five assorted Dritz doll needles. Four of them are of minimal interest but the largest looks just like the needle that came with my 2" x 2" Weave-it loom except that this needle is sharp. I rounded it off pretty effectively using a whetstone. These packages of needles are widely available at national hobby stores.