HR will not provide the document. However, you can provide a reference letter from your colleagues. If you have worked in more than one projects with different teams you would need separate reference letters and combine them in one file.
There is no fixed format for Letter of Reference but make sure to include the following details:
Name, Employee Id, hours/week worked in the Organization, duration (from and to date), Job Title/ designation, job title/designation of colleague, your Role and Responsibility.
The details of the colleagues signing the LoR would state (Everything except signature should be printed):
Name, designation, signature, company name, email id (try giving the work Id), contact number.
You may also add copy of scanned Id card of the colleagues to add credibility to the reference letter (I included in mine).
Good Luck!