The 500 hours multi time can be waived on completion of suitable training, however it involves extra hassle and paperwork (so I'm informed), so the offshore companies generally look for people with more hours (as this reduces the hassle), particularly for ABZ. Bristow choose not to bother with the paperwork & hassle, since they can offload it onto their in-house school. They can't really not give preference to their own school, otherwise what's the advantage?
There are openings with the big 3 for 200-hour pilots (with the Bristow exception above), you just need to be in the right place at the right time. Keep current CVs with all of them. CHC and Bond have both taken on low-hours pilots over the last few months.