I just recently got interested in making painted bow holders, as well. Here is what I plan to do. I'm going to print the letter(s) that I want using Microsoft word. I like the Curlz and the Curly Cue fonts. You can adjust the font size to what you want. I've made my fonts 500 pts before. I bought sheets of blank stencil mylar from Michaels for $10.99 for 3 sheets, but I used my 50% off coupon. Yaaay! The sheets are big, too. Place the printed letter underneath the mylar and trace the letter onto the mylar. Use your craft knife to cut out the letter and BAM...you have a stencil.
You can buy a package of makeup sponde wedges to pounce the paint onto your plaque. They sell the same exact sponges at Michaels in the stencilingl section for like 5-10 for $4.99, but I bought a package of 32 at Target for $1.72. I get my plaques at Hobby Lobby for $1.47 and this week Hobby Lobby's coupon is 30% off of all unfinished wood, which brings it to $1.03 per plaque.
Another method I was thinking might work would be to buy transparency sheets that you use for projectors and run it through my printer and then cut them out. We can figure it all out together. LOL! I hope this helps. I'm going to try this out tomorrow or Wednesday and let you know how it works.