There is no central directory / manager to contact who could give you dozens of referrals. On LinkedIn there are several groups that you might use to ask for more interested parties, e.g. Alfresco Professionals (https://www.linkedin.com/groups/3396116/), Alfresco Freelancers (https://www.linkedin.com/groups/2516405/) or Alfresco developers (https://www.linkedin.com/groups/111865/). I am in all three of these groups, but to be honest, I have never found any value in any of the business network's groups / forums features as most of the time the real experts are not active therein and are typically discouraged from participation by a slew of low quality, sales-y or head hunter-y posts that degrade the experience.
We as the Order of the Bee have offered members of the community the ability to self-register in a Professional Services Network (https://orderofthebee.net/professionals/), but interest in this has been low recently and few members have ever actively contacted us to update their information once registered.
There also is an Alfresco Discord channel (https://discordapp.com/invite/f7XntQN) for more immediate questions / answers with members of the community, if the forum takes too long for you.
One thing I'd like to do is manage expectations - unless you hire an experienced developer for full time availability in Slack, you will not always get your questions answered "instantly". E.g. I am in a sort-of similar arrangement with one of my customers like the one you outlined, meaning I am active on their Slack server and provide input on their questions / discussions when necessary / requested. But since I am also working on regular projects of other customers, and may even be travelling, they cannot expect instant / short-term answers from me all the time, otherwise they'd have to hire me as a regular developer of their team full time, or reserve a certain amount / blocks of time per day to not be working on other projects.
That said, and given how I am already working in a similar capacity for a customer, I would be available to work with you (or other parties who may read this in the future) in a similar manner.