One thing to quickly gain traction [assuming you have a portfolio of samples --- remember portfolio doesn't mean clients had to hire you for it....]

Find companies already using similar illustrations...
Reach out to them telling them where specifically you could help
Show them your work
Offer your services

A mistake freelancers make (and I did too) --- you try and preach to the un-converted.

Waste of time!!!

Reach out to those who already see the value in what you do. Yes, this requires some digging and research. That's what separates the weak from the strong :D