I am in Toronto, Canada and would like to know which governmental
department (or private one for that matter) I should contact in order
to get a list of manufacturers/principals of certain products for
export. Do I need to contact some Ontario export bureau, or is there a
federal agency that I should get in touch with? What is the best way
to find out? The goods I need are usually very specific and not
advertised. For example, right now I need the following parts for
passenger trains: solid wheel disks (3000 units) and tyre steel wheels
(1600 units).

Hi! Thanks for the question.

Canada's International Trade Center provides such a service that you
require which is getting information on certain products for export.
From the website here is the function of this government agency:

"In partnership with the Regional Trade Networks, Industry Canada's
ITCs can help direct you to the existing products and services that
relate to your particular exporting needs. Their mandate is to work
within the Team Canada Inc (TCI) partnership to substantially increase
the number of Canadian exporters, to expand and diversify exports and
to support the investment initiatives of Canadian small- and
medium-sized enterprises (SMEs)."

"Located in every province, ITCs provide a full range of trade
development services and assistance to Canadian SMEs.."

The Internationational Trade Centers are located in different
provinces. Since you are in Toronto you should contact the office
below.

International Trade Centre 
Industry Canada 
4th Floor 151 Yonge Street 
Toronto, Ontario 
M5C 2W7 
Tel: (416) 973-5053 
Fax: (416) 973-8161 

http://strategis.ic.gc.ca/SSG/ig00023e.html (Staff list and contact
info for ITC Toronto)

In case you would like the contact information for other provinces
including more staff list please click on the link below.

International Trade Centers - Contact Info
http://strategis.ic.gc.ca/SSG/ig00008e.html

Search terms used:            
Canada import trade
       
I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
           
Thanks for visiting us.           
           
Regards,           
Easterangel-ga           
Google Answers Researcher

would be better to find a supplier in the country you are looking to
export to.

Most would agree finding the customer is the hard part, if you already
know (have established) the clients, finding a supplier might be a
simple Joint Venture operation with you getting the cut from both
sides for setting up the deal.

Also cover your a..natomy, my dad bought 6 bellydumps from a Canadian
manufacturer, he thought the import taxes were the selling dealers
responsibility. Some young IRS ...hole instead of accepting it as an
honest mistake cost my old man 100K in legal fees and fines. So
beware, have it in writing.

As usual... Sgt. Shultz knows.... Nuthing!

The country I am supplying to does not have manufacturers of these
products. Either way, I started a company that will export from
Canada. We have other branches worldwide that will be competing for
this order, so it is imperative that I find Canadian manufacturers.

I'm not worried about the duties/taxes as I understand those well.

http://1011.com/Countries/Canada/canada.htm

Do a search at dogpile.com "canadian exports" you will get a ton of leads.

http://www.infoexport.gc.ca/ie-en/OtherServices.jsp