There is a Taiwanese manufacturer of some very nice CNC machined aluminum chain ring guards listed as "Driveline chain guard" on eBay. Mounting bolts and spacers are included; has notch to accommodate the pin on the adjacent chainring. I and some other cyclists on another board have been very pleased with them. Available various colors and in larger sizes than you can typically get for BMX (e.g. 53 tooth size). Currently listed example.