Commission rates vary with brokerage and required duties. Normally the rate will start at a certain percentage, which will decrease by 1% each year of the lease. Commission is paid on the term of the lease, the minimum term is 5 years, but it can be longer and commission can be paid for the full term.
My advice is to speak with a few Comercial Brokerages, Coldwell Banker Commercial, CBRE and Lee & Assc are a few you could try.
There are no "standard" commissions as they are negotiable between the parties involved. And, as Anna points out, it's against the law to have a fixed standard. Commission fee should be based on the quality and type of services provided as some real estate firms have a flat fee for their services but they don't give you the same amount of service as a full service firm would.
Hope this helps.
Prudential Connecticut Realty