So, where to get stuff?
The first place I look is Markertek. Shipping is baked into their prices, so there is never an extra shipping charge (for basic shipping). If you are buying in volume, you might get what you are looking for cheaper but for a connector, jack, plug, or cable, Markertek is pretty good.
My "go to" stores
Markertek (for cable and connectors)
Note: they have more available than is on their web site. Call or chat with them and ask
Harbor Freight (cheap tools and some heat shrink)
Amazon (heat shrink and tools)
HomeDepot or Lowes or your local hardware store
MonoPrice (more for pre-built stuff and speaker wire)
Cables for Less (more for pre-built stuff)
LunaShops (last resort as they stuff is slow to get to you and poor quality)
Wirecare (for sleeving)
Newark (formerly MCM Electronics)
Places I haven't used:
Gotham (for wire - see wires)
Peerless Electronics in Louisville (not sure about this one, but it was recommended)
Highend City (cotton sleeving)
VT4C (Cotton sleeving and silver wire, also knobs)
https://meniscusaudio.com/ DIY Speakers
https://www.madisoundspeakerstore.com/ DIY Speakers
https://www.gr-research.com/ DIY Speakers
Sennheiser HD6xx series
Sonic Craft has Cardas connectors for $12/pr. They also have the Furutech FT-2PS connectors for $36.80. Note, the furutech connectos that fit the Fostex TH900 mk 2 is the FT-2PS-F (which also fit the Sennheriser's) ($55/pr- yikes!)
There are lots of HD580/600/650/6xx connectors on Ali or eBay. They used to be $2-$5/pair, but they have gotten a little more expensive.
For anyone building a cable for the Foxtex TH610 or TH900mk2, there are only 2 connectors I'm aware that are designed for these headphones. Sure, you can use a HD600/650 connector, but it's not the same.
The first is the Fututech FT-2PS-F. It's hard to find, and not cheap ($55 on eBay from some unknown dealer).
Update 2019-09-02: I jsut got a pair from Lunashops for $20. They seem to fit well, and look good. Pics coming after I solder.
For the Utopia, you need the Lemo connector. Thanks to Out of Your Head for finding the part numbers:
FGG.0B.302.KLAD52Z - black finish - This is the one that Focal uses, but the black finish is not readily available.
FGG.0B.302.CLAD52Z - chrome finish - This seems to be the most common part and is in stock from the usual suspects like Mouser, Allied, Newark, etc.
FGG.0B.302.NLAD52Z - nickel finish
From Allied, they are $20.08/ea, but the shipping time might be a long time. Markertek might have them in stock, but you have to call them (800-522-2025) as they don't sell them on-line. I got some cheaper ones ($9.21/ea - left picture below) from AliExpress that seem to work. The ones in the picture on the right looks little different, but should work too.
For the HD800, there are a number of options in the US for pricey tips. I got these from Lunashops via AliExpress ($21.88/pr-shipped). They are more expensive on the Lunashops web site. Be careful with the pins as you solder the wires. I used a vise to hold it, and I squished the brown round base a little, and it didn't fit back in. Use the more delicate clips from a helping hands to hold the pin while you solder.
These Eidolic HD800 connectors aren't cheep, but they have solder lugs! Soldering the HD800 or Lemo connectors is quite difficult, so the solder lugs on the Eidolic's might be worth the cost to you. These are from Double Helix Cables, but others sell these connectors too.
RCA Connectors. Man, what choice. Here's a sampling across the reasonable price range. Also, here a Male RCA Plug Shootout article.
Anti-vibration pads. DOn't pay through the nose for them! Get there here: https://www.supplyhouse.com/Pads-11752000
check "under $1" and "$1-$5" to see the range. the 2x2 work great. Buy a couple of dozen, since they are cheap. Give 'em to friends!
Need a 3.5mm and 6mm plug all in one? Check out the HICON HI-J3563S from Sommer Cable. Also, AliExpress has this one.
Contact infoSommer cable America, Inc.131 Stony Circle, Suite 500| Santa Rosa, CA 95401E-Mail: email@example.comTel. Main: +1-707-200-4020 | Fax: +1-707-284-0618
3.5MM Stereo plugs:
On the budget side:
note: free shipping from Markertek
On the "audiophile" side, but still reasonably priced:
note: plus sound charge a little for shipping
Or full on audiophile:
note: I've never purchased from Moon, but they are reputable.