No, you cannot claim a GST Rebate on these items as a subcontractor. If you were an employee and claiming Employment Expenses on items which you used in the course of your employment, and, your employer issued you a completed and signed T2200 - Declaration of Conditions of Employment form, you could apply for the GST370 Rebate.
As a subcontractor, you should be reporting your income as "Self-Employed" income on a T2125 - Statement of Business Activities. Only GST/HST Registrants can claim Input Tax Credits (ITCs) on expenses incurred.