The smallest numbers on this sheet (also available in black), are still slightly too large for a 1/48th scale Bf109 Geo. I'll be using them on Bf110s and a He111, which, depending on factory, used larger, white numbers.
Some of the very small scale 'wargames' decals, used for tank turret numbers, might do the job, and I've used some on a Ju-88 (the sheet also includes swastika flags, useful for 'kill' markings), but I'd have to check the actual size, and if they're still available.
I'll be making my own decals for all the Bf109 Wk. Nr, as I have in the past. Once the typeface is selected, and the number created, it's imported into a 'Word' document, reduced to the required size, and then duplicated a couple of times to make spares. The resolution and density is not great in this tiny size, but, being so small, it's not really noticeable once on the model.
I need to find the notes I made on which typeface I used for what, so I get the correct (or near as dammit) size.
A method I used years ago, before I had a computer and printer, was to use a fine 'Rotaring' draughting pen and black ink, and 'draw' the numbers onto clear decal sheet. The results, of course, are only as good as your ability to write small characters neatly and consistently, but again, being so small in this scale, once on the model, they're acceptable, and better than an empty space.
Of course, there might be suitable numbers available for Bf109 W.Nr. in smaller scales, such as 1/144th, but I haven't checked that area yet.