There are some yellow LED single pole BA20s on fleabay. The first one only draws 2 watts and supposedly uses Cree LEDs (US). Both are slow boat from China.
1PC Yellow BA20S 5730 12 LED Bosch Car Light Vintage Bulb Front Rear Lamp 6V 12V | eBay
2 X LED BULB 12V BA20S B11 AMBER CAR OLD SCHOOL VINTAGE REAR FRONT LIGHT LAMP | eBay