I believe the guages are standard automotive guages. Would suggest your local Advance Auto. Would also look at guages on ebay first to get an idea what is available. There are TONS of options, many of them look pretty darn cool and don't cost alot. If you get them as a set (IE Guage and Sensor together) they are sure to be reasonably accurate. Note that all the guages are electrical guages (not mechanical).
Hope this helps!
79 28' Mariner twin inboard V-drive. SW Lake Erie: Maumee Bay & The Islands
All the gauges are standard sizes, and can be found a lot of places. Both marine and automotive should work, but as Rock just said, get the sending units as well.
I had the same problem with the warning lights. Went down to Radio Shack and found some small red panel lights (12V). Had to open the hole and little, but looks good. (did all four so they match). I also has a sign company make new dash panels (four) that contain the switches, as mine had all the writing worn off.