I'm definitely not a font mapping expert but we've run into this issue frequently with one customer who likes to create their own fonts.
What we've done is basically identify a suitable PC based font that matches, or closely matches, the actual font.
This we add a FGID for if there isn't one (csdef.fnt near bottom of file)
eg. 3840=Arial,Modern,MED,0
Next we add the charset (top of csdef.fnt)
eg. C?AR08NP=3840,80,73,0,0
? is a wildcard. This will use the Arial FGID to represent the font with height of 80, width of 73, no strikeover and no underline. Again we've had to play with height and width to get the font to look correctly on the form.
As for code page (cpdef.fnt) we've only had to define three of those.
Two were easy by simply defining it to use the code page id of 37. eg T1OMNI=37,ANSI
The third code page was a nightmare as I had to find the nearest matching code page using the old *.cp files that used to come with the clients then write an output exit that changed the remaining codes that didn't match to match those in the code page.
My suggestion would be to start with TIGMCUSR=37,ANSI in cpdef.fnt and then work with csdef.fnt definitions to get it to display correctly.
Hope this helps a bit.