I saw on Lazada cycle racks for cars, but cannot find them now.

Where can I buy one that fits a saloon car?

theres a group called Bangkok hash house bikers, they've got a website and facebook page, its a mtb cycling group that meets once a month and a lot of the riders have various types of racks o I suggest contacting or posting on their facebook page and im sure youl get plenty of responses about them and might even pick up a decent second hand one if you ask if anyone wants to sell.

Cromozone are selling bike racks that fit to most cars, you can find the details at bicycle Thailand website. I bought one and so far its fitted on a 95 CRV, Jazz, Soluna and a nissan saloon car, as long as it doesn't have a silly spoiler on the back of your car, you are pretty sound with it. Its called the 'Hollywood' and its about 3k. Cromozone is up by Ramintra KM8 and the Namawin intersection, but like I said bicycle Thailand has the web address, telephone numbers and stuff.