Is there such a thing as an advisory CTO? And where do you find one?

I need someone that I can ask for advice on app structure, how to set up the queuing of jobs, API design and database design / optimisation. My coding is alright and I can hire developers no problem and break tasks down, but I need an experienced developer to lean on for advice from time to time (around 4 hours a month I'd guess). I use "CTO" rather than mentor or advisor because I'd like the person to be part of the team and to believe in the project. Mentor and advisor seem too abstract somehow.