Team → Subcontractors covers both directions of subcontracting:
Bringing subbies in: invite a subbie by email — they get a free SwardOps account locked to working with you (they never see your customers or prices). A firm that already uses SwardOps links even faster: they give you the subbie code from their own Subcontractors page. Per subbie you can offer a job or ask for a price, and they respond in-app.
Their invoices: subbies invoice you through SwardOps. CIS is handled — set each subbie's rate (0/20/30%) and every invoice shows gross − deduction = pay, on both sides. Much grounds work sits outside CIS entirely, so there's a company-level switch to turn CIS off — invoices then just show the gross.
The work board: post a job out to other local SwardOps firms (title, details, budget, postcode — never the exact address), and set your own "looking for work" radius so you're pinged when someone posts within, say, 40 miles of your yard. Registering interest sends the poster your subbie code so they can link you in one step.