They actually did approach mobsters like Bulger, Joe Murray, and Pat Nee in Boston and Ed Loney and Johnny Berkery of the K&A gang in Philly. Also John McCullough, who ran the Roofers local in Philly who was a semi-gangster and semi-legitimate guy used to raise money and actually hire IRA members on the run in Philly.

If I remember correctly Harry Fitzsimmons was with the Provos and not the Real IRA.