Is it possible to have any CAN baud values? e.g. 507 baud
If not, on what basis is the standard values are derived?
If you are building your own network, yes. All baud rates are valid provided every single device on the bus is using that particular baud rate.
If your bus has devices which are beyond your control, use only standard baud rates, otherwise you will generate error frames.
Standard baud rates are 125 kbit/s, 250 kbit/s, 500 kbit/s and 1 Mbit/s.
I don't know if there is a standard way to "derive" baud values, but most devices come with these baud rates.
Also, you can implement your own algorithm to detect the baud rate of the bus and then configure your device accordingly. One of the methods is described in section 5.1.15 of the docuemnt Introduction to the Controller Area Network (CAN).