If you are looking for a gauge for tuning, I'm sure there are lots of options like the app you found.  However, the first part of your post sounded like you want a dash mounted gauge.

As you have probably found, most air/fuel gauges are digital with loud colors.  There are some analog gauges with white or cream colored faces but they aren't likely to have needles to match your magnolia gauges.  Visit www.egauges.com and www.egaugesplus.com and browse through their offerings.  Unfortunately that will mean going make by make, then series by series looking for gauges that are similar to the ones in your car.  Also, a number of people here have bought speedometers from www.speedhut.com  Speedhut will make "custom" gauges and may be able to provide you something very close to your car's gauges.

I installed an O2 bung on my exhaust pipe but have yet to install a gauge. I have a set of Smith gauges (temp/oil press/amp/tach) with magnolia faces that I'd like to match, but all I'm able to find O2 gauge-wise are garish looking things with neon beer sign illumination. Not the look I'm after. OK, there are a few white faced gauges available, but I'd much prefer one w/ a magnolia face.

As as an alternative, this looks pretty nifty [O2 Gauge App]. Has anyone had any experience with this or something similar?