Harware engineers, mechanical engineers are less likely to contract. You you might have a better chance finding is a contract manufacturer or contract design firm.
You will have a hard time finding what you are looking for on a contract basis because:
1. Most good mechanical engineers have full time jobs (which are secure)
2. Hardware engineering varies greatly, and can require a huge investment in research and labs, this is very different than software.
If you are price conscious do your research in Singapore, Taiwan, S Korea and other south east asian countries that have a good reputation for this type of work, and respect your your property rights.