I found this IC, which can drive 64 LEDs or up to 8 7-segment displays, which means only two of these are need to drive the main part of the MCP, or 3 if you want the course selectors. I'd imagine that any 7 segment display would work, so if you could manage to separate your linked voltage meter from the display, it would work beautifully with your MCP.
As for the LED buttons, I found the buttons you're using from this article, which includes a link to buy them from conrad.de, but they're out of stock with no picture, so I'd imagine they're not coming back. A quick search on ebay for LED momentary switch reveals only metal buttons with blue or red LED rings, which frankly aren't good enough and would be ugly against the grey of the Honeywell MCP in the 737 Classic, thus the saga for buttons continues.