In the last 90 days, 0 listings have been posted online, which means new availabilities most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About Inf% of the available leases in the Rosemead are subleases, so you might be able to snag a great spot on a short term. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,450 sqft. Most buildings in this area were built in 1982 and are Class B.