#1. Bulbs are not your problem. You have plastic housings which are a solution to rusty housings, but, The problem I see is that you have some kind of cheap melting plastic which needs to be made out of metal or ABS. Finishlineaccessories.com can help source the proper Lucas lamp.
#2 LED Bulbs. I have a PN for you which is outstanding.
Motorcycle LED Lighting by Custom Dynamics
GEN-20-R-1157 Its a standard bulb which is in a circular array. It's very bright and has a brighter flash circuit. But, here is the kicker, you need to put a load on your blinker circuit for your flasher to work properly. The LED lights draw only a few milliamps current and the flasher circuit is designed to work with incandescent bulbs of only a few ohms resistance. i.e. 12 volt bulbs. It's not a problem, they make loads which you can hook up in parallel to the blinker lamp. Here is the PN for the flasher replacement option. "EDFR"