My multi entry Type B non immigrant visa expires in early March. Can I get an extension through immigration? How long?

Any other options available to extend the stay before I must do another type B??

7 days maximum at Thai immigration, and probably requiring sight of air ticket out of the country within that timescale. You can apply for extension of stay based on employment if you meet the requirements. Otherwise it will be a new Non-B visa from consulate abroad.

KL and Penang will issue multiple entry Non-B visas within the region with company documents and at least 8 months remaining on work permit. Penang also requires company to have minimum registered share capital of 8 million baht. If remaining time on work permit is a problem then suggest you consider obtaining in Perth. More information on Perth consulate website here.