Searching for Niche Vertical Market Software Companies in the UK

Does anybody have some good ideas about how to build top of funnel deal flow for finding niche VMS businesses in the UK?

I'd love to find a small under the radar $0.5-1.5m EBITDA businesses serving small niche markets with high recurring revenue and sticky customer base. Boring, unloved, stable cashflowing and no reason for users to defect to a competing software/new entrant because "it just works".