I found a relatively inexpensive vendor of "the good stuff" on Bay. I think he was based in Maryland. I've purchased from him twice over the years. Cable appears to be mil spec, not Chinese counterfeit goods.
That said, unless you have some use for leftovers and are content to over-estimate your needs, I'd try using weed eater string or similar to mock up my cable runs in place in the airframe and get a material total. Add 5% for error, and a few more feet for mis-cut ends during the soldering/crimping process. I don't recall the total in my -10, but since these planes are custom-appointed, it won't generalize anyway. I have runs for ELT, XPDR, ADS-B, two comm antennas and a VOR antenna with coaxial balun, 2 GPS pucks, all likely located in areas where you would not choose to put yours. For some of these, the cheaper RG-58 or RG-8X would work as well, others are high enough in freq that the lower loss 400 cable is definitely indicated.
With shipping charges and delays in progress, it's cheaper to buy 10' more than you need than it is to buy 1 inch less, the first time...
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