Registration applicability in case of contract with govt agencies in other state

No required deducted TDS. if supplier has only one business as u mentioned above. then as per my knowledge no registration is required

As per SOP in cbic site : The provisions of TDS would not apply in this case irrespective of the contract value as the Place of Supply and Location of Supplier is different from the Location of Recipient.

So only TDS will provision will not applicable. Else as per Section 22 of CGST Registered person in GST can supply goods or services or both from state where he is registered. No need obtain Registration in Gujarat.

But dealer is providing different service which is not related to it's existing business.

Then obtain registration in Maharashtra

It ca be provided under existing GSTN .