There is no specific place to go to... a lot of it simply comes from working within the industry and learning the key players. My company doesn't buy/sell electronics, but the factories operate more-or-less the same.
Going to Alibaba is like shopping on Amazon. You wouldn't go to Amazon to purchase bulk (> 10,000) pieces of some item... you certainly aren't getting the best deal. Amazon takes a cut (so does Alibaba), and retailers listing there have catered their prices towards end-users (so significant mark-ups).
If it were me, I'd post on electrical engineering forums and ask who people recommend for fab jobs. Sometimes a nice supplier/distributor will tell you who they use for fab jobs (but a lot do tend to guard this).
Alibaba just isn't the best way to get the best price...
You make a good point, though. The shell size (DB) is the same and you can purchase shells separately. The problem devolves to getting the contacts (it's a standard item you can buy easily) and molding a custom insert. For small quantities, it seems like he could do it himself. The mold shouldn't be difficult to make.
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Even easier would be finding out what material the insert is made of and getting the connectors milled to shape and drilled for the contacts. Fun problem!
If you've got a DB19F floating around you could even make a jig to hold the pins in place in the exact configuration you need, then simply epoxy them in place.
Would you accept a consulting gig if it was a one-off job, required a 2 hour commute in both directions, and you expected to be onsite for only 1 hour? Maybe...
You might accept if you were really desperate to get any job, or you might accept if your contract pays for your commute time and expenses. But if neither of those conditions are met, you would probably turn it down as it wouldn't be worth your time.
This is over-simplifying this a bit, but it's along the lines of how the factories view this sort of thing.
The author is asking them to spend more time and expense tooling up than they will in actual production (your 4 hour commute round-trip). If they were already tooled for this component (you lived in the same city), then they'd be more open and provide a better rate (you charging just your on-site fee). But since those conditions are not met, they will make you foot the bill for tooling (you charging for your commute and expenses), especially since the likelihood of some other buyer coming along and commissioning this component are very slim (the consulting gig is a one-off).
One thing you can do is go to brokers. These people buy old stock from suppliers but also buy old stock from manufacturers who go out of business or who no longer meed the part.
The parts you get are espensive and don't have the same chains of paperwork and may have been mishandled.
There is a problem that you can end up bidding against yourself and driving the price up.
Going to Alibaba is like shopping on Amazon. You wouldn't go to Amazon to purchase bulk (> 10,000) pieces of some item... you certainly aren't getting the best deal. Amazon takes a cut (so does Alibaba), and retailers listing there have catered their prices towards end-users (so significant mark-ups).
If it were me, I'd post on electrical engineering forums and ask who people recommend for fab jobs. Sometimes a nice supplier/distributor will tell you who they use for fab jobs (but a lot do tend to guard this).
Alibaba just isn't the best way to get the best price...