the ghetto fix is to buy a halogen security light (obviously the DE type) from HD or lowes and take the end caps out from the fixture. for a 150-250w you're going to have to take out the endcaps and cut the center brace so you can fit the bulb. also, you'll have to chip away at a portion of the ceramic to make the bulb slide in. very ghetto but no one can look at it and see what you've done. plus, it's locally available and only around 10 bucks.
the type i used to retrofit a 70w de mh was a Regent brand 300 watt halogen floodlight, model EQ300WL. goodluck.