well perhaps by category on link exchange sites like
Marketing webmaster tools search engine submission back link building and over 5 gig of downloads.
There are 75 link exchanges listed at
marketingwebmasters.com
Otherwise google subject + contact, subject+traffic or subject+advertising etc and look for reciprocal traders.
The real thing is the personal touch to the connection email very difficult to find these links often good to buy them by exact subject on
https://www.fiverr.com/s/6ksurx