Commercial Multi-Family purchase contract if using a commercial realtor...

No. You can have your own Purchase and Sale Agreement (contract) drafted. Most real estate attorneys use their own contracts over Realtor board approved contracts, especially in non single family residential transactions. Your commercial realtor may have a contract that he/she can customize, but it is recommended that you have an attorney review any contract.

I agree with Eric T.
Whatever form you use make sure YOUR attorney ensures that it represents your best interest. You can use the Realtor form but you may have to mark it up.

TO BE CLEAR, A real estate broker is not necessarily affiliated with a Realtor Association: MOST Residential real estate brokers seem to find it helpful -- Commercial Brokers usually do not ...

A specific Single-Family ( or 1-to-4 family ) Residential Purchase Contract form may be REQUIRED by state law, depending upon each state, by those states' real estate governing
agencies -- NOT by a national or local REALTOR ASSOCIATION, BOARD, or any such affiliation.
To my knowledge, their are NO STATES which require any specific contract verbage or form as it applies to COMMERCIAL TRANSACTIONS. Real Estate Brokers in MOST IF NOT ALL STATES may "broker" BOTH residential AND commercial property purchase transactions. These brokers may well have legal assistance available to them which allows them to offer a "recommended"
purchase contract form with "recommended" contract verbage. However, such recommendation
comes with the caveat that the recommendation was offered for the benefit and convenience of said BROKER, and not necessarily in the best interest of either the PURCHASER OR SELLER.
ALL PARTIES TO either RESIDENTIAL or COMMERCIAL TRANSACTIONS should seek for their
OWN INTEREST legal representation with a FIDUCIARY responsibility to their OWN INTEREST.
There.

As the buyer - you are certainly able to submit an offer to purchase a property on any contract form you may wish to use. There are many available and you can purchase some at office supply stores and the like. You'd best be served by utilizing the services of a competent real estate attorney to review any document you may wish to use - whether one you write yourself, buy at the office supply store, use one prepared by an attorney or use a form promulgated by your state / area real estate group. You mentioned use of a commercial REALTOR - which is a term applied to a licensed real estate agent or broker who is a member of the National Association of REALTORS and perhaps through a local commercial group. Generally they have access to excellent commercial contract forms but again you should have your attorney review them to guide you towards an offer that covers what you are wanting to accomplish in your purchase. An experienced commercial real estate agent will be able to assist and guide you through this process. Do keep in mind that a licensed real estate agent or broker is NOT licensed to practice law (unless they also have a law license) and thus can not write clauses or modifications to a contract and can not interpret contract clauses without running afoul the their own license requirements that dictate against practicing of law without a license.