You'll want to explore a number of potential Independent Sales Rep firms in order to find a good match.
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Interesting question... would love to see some answers.
What were their SEO keywords? Since specialisation and niches are the key to knowing who to target I would suggest they start there.
Where they target "magento developers"? Then they were not specialising much - try targeting 500 digital agencies in the USA and offer to sub contract their maintenance work and updates (ie keep old clients happy)
Where they targeting industries? Such as ecommerce for hair products? So start by identifying all the hair websites out there, collate a report on the quality of ecommerce, security vulnerabilities, then cold call to sell that and then follow with your services.
Expand into products - magento addons, etc. if these guys are any good they will have three internally used anyway
Do not hire lead development companies - never heard anything good of them.
Do not hire a bizdev person till the CEO can do the job themselves so knows what to ask for.