I am a Technical Director at a major studio and have been in the industry for over 20 years. LinkedIn is your best bet. Mobile developers will come to you (even when you don't want them to). If you make a public post asking for mobile game developers you will very likely get inundanted with offers from every corner of the earth. You can also make a request on Twitter using the tags #indiegamejobs #gamejobs and #gamedev and mobile game developers often watch those tags so they can respond (even when they're not desired) to posts where people are looking to get game ideas developed. Be careful of companies which show mostly web development experience -- they will also build games for mobile devices and that's not what you want. Look for companies that use Unity, Unreal, or similar engines and have a portfolio of games still live on the app stores that you can play and check our for quality.

Feel free to call me if you want to chat further!