The 12 volume "RGS Story" collection is a useful resource. There are, of course, many many photos. The main problem is that most of these are taken from a distance, with the car or engine at an angle. Furthermore, the 'type fonts' vary by date, lettering flourishes, spacing between letters and words, etc. And good luck estimating the size of the letters. The pilot numbers may also be metal plates, with curves made up of 45-degree segments.
I did just such a search for the forthcoming RGS engine No. 36. Just finding a good "3" and "6" was difficult. It was particularly hard to find a good "6". And the middle nib in the "3" seems to have a different flourish in every photo. The "Rio Grande Southern" on the tender, shown in the single known photo of No. 36, is grainy, dim, sharply angled, and distant. These were all block letters, with the first letter in each word slightly taller, perhaps 10" versus 8". I believe there was a slightly wider spacing between words, while other loco photos show no spaces. Lettering on other locos varied by car/engine and date.
So, don't expect to find a perfect, antique, type font. Good luck!