Some links where you can read about manufacturing pcbs - even with downloads...
Order a "blank" PCB:
http://www.clockworkrobot.com/shop/
http://retroelectronik.com/en/cartmodding/76-vectrex-replacement-pcb-for-repairprototyping-test-or-cart-modding.html
"Simple" PCB design done by Frank Buss:
(also download for eagle)
https://hackaday.io/project/28295-vectrex-cartridge
https://blog.oshpark.com/2017/11/22/vectrex-cartridge-board/
https://github.com/FrankBuss/bloxorz
"multicard/flashcard" PCB design done by ALeX Kazik:
(also download for KiCad)
https://github.com/alexkazik/mucarex
https://alex.kazik.de/312/mucarex/
Explanation how to do a "simple" multicard:
https://www.harmlesslion.com/text/vectrex_multicart.htm
dual port SRAM Cart to interface to an Arduino Mega. - final version missing (also download for eagle)
http://vectorgaming.proboards.com/thread/1276/dual-port-sram-cart
Purchase new PCB with ROM service:
http://www.ombertech.com/romprodindex.htm