There are several classes of mortgages available: residential, investment, and commercial. There may a couple of others, but these are the big three.
Residential is obviously your owner-occupied house. Investment and Commercial can sometimes be used interchangeably, but typically investment is more often used to describe non owner-occupied houses bought for investment purposes. Commercial is typically used to describe most everything else, such as: warehouses, apartment buildings, retail buildings, etc.
So if you are interested in buying an apartment building, or a retail or office complex building, then you are looking for a commercial mortgage. Part of your research into whether to even purchase the property must include some idea of interest rates, etc. You want to know whether you can afford to make the monthly payments that will be required. A website such as Realty Rates can help you by giving you fairly current commercial mortgage rates for various types of property. This particular website could be helpful because it also provides you with quite a bit of related information. It also breaks down the information by building types.
Once you've done your basic calculations and have decided to move forward in your purchase, now you need to get more specific. You can obviously go directly to just about any lender out there. Most residential real-estate lenders also have a commercial division. Ask your current home mortgage holder where to start. Many banks and credit unions also have a commercial lending division. Again, start with your current bank. They may be more willing to work with you since you already have a relationship with them.
If you personally want to check with quite a few different choices and shop around for the best commercial mortgage rates, the internet is probably the place to go. Websites such as C-loans.com, Business Finance, or Buyer Zone all provide you with matches tailored to your specific scenario. Be aware that this may subject you to phone calls from interested lenders. Buyer Zone appears to ask specific enough questions to be useful, but doesn't require you to give personal contact information in order to get matched with some potential commercial mortgage lenders. Of course a potential match in no way constitutes a guaranteed offer of financing.
You may also want to check with a commercial real estate broker. Look for one that isn't tied to a specific company. That way he/she can search for the most suitable lender for your situation. Be aware that you will probably pay a fee for their expertise, but it may be worth it. Some people don't have the time or inclination to do their own searching. Also, the broker may sometimes know of great financing that the average internet search may never be able to locate.
When finding a commercial mortgage rate, use the option that you are most comfortable with. Regardless of which method you choose, you should be able to get a good idea of what the going rates are for your specific type of purchase.