Newark page for the DE24657:https://www.newark.com/cinch-connectivity-solutions/de24657/junction-shell-size-de-steel/dp/45F986#anchorTechnicalDOCS
The problem with this backshell is its coating of yellow chromate (apparently there is some zinc too). This may not be vacuum chamber compatible.
They make a clear coated one but it's oddly enough clear chromate.
Here is a link to the PDF of the full CINCH catalog. The DE24657 is on page 9: http://www.farnell.com/datasheets/671881.pdf?_ga=2.28253820.1338228539.1551109163-1653510471.1485545260
There are a few stamped sheet metal backshells that can possibly be used for rear panel mounting. These include the 3M 3357 (held together with a festive plastic nut on the back so it's not vacuum compatible), some two piece TE emi hoods with a very thin front channel (https://www.mouser.com/ProductDetail/TE-Connectivity/1-2308340-5?qs=%2fha2pyFaduj2ev0%252b1%252bYgy0scmK3sARzLM8%2f4k84RMN4W%2fcKQ6Zc%252bZQ%3d%3d), these custom one piece backshells: https://www.stahlmetall.com/pages/d-sub-rectangular-large-cable-entry-emi-rfi-shielded-backshell-metal-nickel-zinc-plated and something similar from the more reputable Plamco: http://www.polamco.com/bt-series-291/
Glenair has the super deluxe stainless-steel panel mount backshell series 500T009. https://cdn.glenair.com/catalogs/rectangular-connector-backshells.pdf In their same day stock the part number 550T009M1R3L0 is the E size, with no EMI gasket and strangely compatible with our milled panel thickness. In Octopart it shows that Powell sells it for $180 each in quantities of 10.
CINCH also made this wonderfully primitive looking single piece rear mount backshell called the 217 which includes designs with a straight exit and 4-40 tapped holes, but nobody sells them and they are probably discontinued by now
Here is a catalog page for one at Allied, which is linked to by a page for an electronics distributor in India: https://www.alliedelec.com/product/cinch/21715h-r/70544301/
Here is a fairly new looking datasheet for the 217 that still doesn't go a long way towards explaining what the weird extra piece is for: http://www.farnell.com/datasheets/22727.pdf
Octopart has some hits for the 9-pin version, including Allied and Arrow (both not in stock): https://octopart.com/search?q=2179H
The arrow link is revealed to be a "direct ship" scam: https://www.arrow.com/en/products/217-9h/cinch-connectivity-solutions
