Congrats on the car. This is a very sturdy car and luckily if it is well cared for you won't be needing much stuff. For body parts you will have to look in scrap yards. For Engine parts the situation is better. The following vehicles use the same engine.
-Hyundai Accent DLS
-Maruti Esteem Di
-Maruti Zen D
Your best bet is Premier as it is the only vehicle still in production. Also the fact that the 309 was manufactured bu Premier itself means they're more likely to support you. BTW
is the photo you posted one of your car? The car in the picture is a LHD and the plates look like some Euro ones.