Zanen Electronics sells cap-kits (Monitor Get Well Kits as they call them) for numerous arcade monitors. They don't have a website (yet) but their contact details are below.
Here's some info from them:
Monitor repair kits take care of picture warping, blacking out, smearing, low brightness and brightness problems, poor regulation, jail bars, vertical shrinking, etc. Call for FREE technical help with your monitor problems. All kits come with instruction and are easy to install.
46 Parklane Dr.
Ransom Canyon, TX 79366
Visa and Mastercard accepted. Discount! Buy any 10 kits and take $1.00 off each kit. Free shipping for orders over $25.00
They also accept PayPal, mail them for more info.