That depends on whether the airplane is Part 91 or 135 operated. The Part 91 Lear 25 I was on only required a multi-commercial instrument pilot with no specification as to hours. However the company's Lear 35 requirements were different becasue it was used for charter in that case they wanted something like 1500TT, 500 multi and 250 turbine, 100 in Lears. Now the big mystery is how the heck do you get that? I figured i could at least build the 100 in type by riding in the part 91 Lear. That was the plan anyway until the owner sold the airplane after I only got 20 hours.
The other recent roadblock when it comes to anything Part 135 is this schtick about "must have a current 8410" and the ever popular "must have attended FlightSafety or equivalent training in the past 12 months in type". In other words, they want a "no assembly required" pilot whose ready to start tomorrow and does not need any training. Kinda hard to meet that standard...especially is you've never worked for a 135 outfit before.
Your best bet is to somehow find a Part 91 operated airplane. Insurance companies have been known to require operators of even the SP models to have a crew of two. The question comes down to then, are they willing to pay for your training to sit there SIC, or do they also want a ready-made pilot? Good luck to you.