Much will depend on the make model and age of the cooker - spares may be available but the manufacturers are smart - they want you to buy a new cooker after a few years - there is little for them to gain by producing spare parts year after year.
On your cooker will be a sticky label - a rating plate - often low down and often somewhere on the front face.
Take the details of Make & model and check out spare part suppliers on the web - 'phone and find out if spares can still be had.
Good luck...
Peccavi
November 2010