I made my own pressure gauge and holder. I bought the NOS or Autometer adapter that you screw into the place on the fuel line where the schrader valve goes. I ran a piece of SS (stainless steel) braided hose to a brass T fitting that I mounted on the fender well by the MAF. I made a mount bracket out of aluminum angle I got from Home depot and bolted it to the fender well. Then I mounted the brass Tee to it with some machine screws and a plate. I sandwiched the brass Tee between the aluminum angle and a flat piece of aluminum that I trimmed off the extra aluminum angle. Three screws laid out in a triangle pattern go through both pieces of aluminum to clamp the Tee in place. I used a cheap industrial gauge from MSC Direct ( http://www.mscdirect.com/PDF.process?pdf=4588&Keyword=Y ). It works great and was cheaper than anything Summit had.
If you look through the MSC Direct catalog, you can find any type of gauge you want, including liquid filled. You only need a liquid filled gauge if you mount it directly on the engine. The liquid filling dampens out the vibrations.
You can buy the Autometer Stainless Steel braided hose for like $60. Or a local shop that makes hydraulic hose assemblies can make it for you at a cheaper price. Ordinary low pressure hydraulic hose can be used in place of the Stainless Steel braided hose, the Stainless Steel braided hose just looks nice. I got mine for $4 at a place that sells industrial and military surplus parts of all kinds. The Stainless Steel braided hose goes for about $3.60 a foot and the fittings are probably about $5-$8 each. You can make your own and save some $$$, the shops may have a setup or labor charge to fabricate the hose assembly.
Have you tried looking at Lowe's or Home-Depot? I got a T-fitting there so I could run my fuel pressure gauge and fuel line for the nitrous from the valve on the fuel rail.
Use one of the fittings above that has 1/8" pipe. Then visit your local auto parts or hardware store & find a brass 1/8" pipe elbow.
As a rule, I do not recommend mounting the gauge direct on the fuel line. It is too easy to break the adapter, gauge or both. The vibration also puts a strain on the mount and can casue the threaded boss on the fuel line to crack & leak.