Tier 2 Sponsorship for client based projects

Currently I am working in UK with Tier 2 ICT dependent visa (spouse visa).

Now I am working under fixed term contract.
My Hr confirmed me due to your visa validity we can't mention permanent in your offer.

I have already approached them about visa sponsorship but as they are saying I am based at client location they can't provide me sponsorship.

My employer has asked me to check with any legal firm if sponsorship of Tier 2 Visa can be provided for a client based Employee.

Thanks