Here is some data.
DH Gate: G4 245 MD LED, 240-288 Lumens, 12V (no indication of max voltage), no wattage indicated, $6.27 each
LED Leightsworld.com: HK-G4-12SMD 5630-X, 200-250 lumens, 8-30V DC (have to let them know when you order you need this voltage range or they will ship 12V unit), 2.9 watts, $11.50 each plus $8.95 flat rate shipping
Lily LEDs: G4 9x5639, 200 lumens, 10-30 V DC, 1.9 watts, $8.50 each with $25 min order, $11.00 shipping
Marinebeam: G4 12 LED Force 12, 170 lumens, 10-30 V DC, $20 each, $6.95 shipping
Hero LEDs: LB-SG4-9T-12V, 200 lumens, 10-30V DC, 1.8 watts, $4.64 each but have to order 5 = $23.20. Shipping Free
G4 LEDs.com: G4-12-30A, 240-264 lumens, 10-30V DC, 2 watts, $2.86 each, shipping $10.00
COMMENTS:
All of the companies except Marinebeam are China based. I am not sure where Marinebeam's bulbs are actually made. The company is located in South Carolina.
I ordered bulbs from Hero and G4LEDs.
I will report my results after I receive and install the new bulbs. I would like to have one of the Marinebeams to compare since others have indicated good success with them but I will wait and see how the ones I ordered work first.
To Ralph's point above I currently have first edition China LEDs that cost about $2 each and are rated at 10-30V. I have never had any problems with voltage tolerance, dimming, etc. So I anticipate no problems with the new LEDs I will be trying out.