One of the great challenges of pin loom weaving is that while the looms last virtually forever, they are useless without the right needle. Happily, I am here to report that there are an increasing number of good needles available to you. Keep in mind that a 4" pin loom works best with a 6" rounded tip needle. The 2" pin loom needs a needle that is about 4" long with a rounded tip.
Here is a list from my exploration of needle resources. I doubt that its complete, I hope that you will consider adding on any information you have discovered about needle availability.
1) Replacement needles from Schacht Spindle Co., makers of the Zoom Loom. Many Zoom Loom sellers will likely have 6" weaving needles in stock or be able to get them for you.
2) 6" Trapunto needle. Trapunto is a style of quilting/fiber work that calls for a long needle with a blunt tip. This needle appears to be exactly the same dimensions as a pin loom weaving needle. When I did a search online I found the Havel's Sewing website, which offers both trapunto needles and my next suggestion. There appear to be a number of online sources for trapunto needles.
3) Ribbon Weaving Needles. This is a set of three needles, 4", 6" and 8". I bought this set locally but they are also available from Havel's. (I do not have any kind of relationship with this business.) These needles are also available from a variety of online sources.
These needles have a rectangular cross section, they are very strong and have a blunt, rounded tip. Their dimensions are 1/8" wide and 1/16" thick and they do easily fit through the pins when held on their side. The 4" needle works beautifully with a 2" loom. Because they are stronger than a normal pin loom, I am tempted to use them when I am working with a person new to weaving who, I fear, might bend my weaving needle. This set also offers an 8" needle which is very handy if you have a 6" pin loom or any larger loom. I have had a few weavers note that they like to use a larger needle on the 4" loom because it is easier to handle and hold on to.
4) I found all of the following needles in local big box craft stores. The dimensions are correct for weaving on pin looms but all come with sharp tips, which means that you do need to round off the tip using a file or whetstone.
This set of three decorator needles includes one 6" needle with a pointed tip. I find the other needles too thin to be of much use.
5) This set of four upholstery needles come in 6", 8", 10" and 12" lengths. The two largest seem too unwieldy to be helpful. The 6" needle works perfectly on a 4" pin loom, once you round off the point. I normally use this 8" needle on my 6" pin loom.
6) This last entry is for the 2" pin loom. This is a package marked Doll Needles found in the notions department. It contains five needles, but the only one that interests me is the one large 3 3/4" needle that works perfectly with the smallest pin loom.
There have been several occasions where all of the notions, including these needles, have been on sale for 50% off. Since I am teaching classes with these looms, I often swoop in and pick up a bunch of packages.
When I started using these looms a number of years ago, there really was a sense of looking for a needle in a haystack. Now I am happy to report that we have finally have haystacks full of needles-- perfect for pin loom weaving!