welcome to the forum!
The best way to get loads more track is either:
a) e-bay
or
buy more sets - even if the power base etc is not going to be used, or better still sell those bits. Analogue track is compatible, though not the power base. I am not sure if it makes sense to buy another digital set for the LCs and digi cars
Scalextric also do 'track expansion' sets with various bits of track in them.
The best way to get loads more track is either:
a) e-bay
or

Scalextric also do 'track expansion' sets with various bits of track in them.