Welcome janice!
Do you mean it it is too heavy to shift about or your stage won't take the weight?
I would imagine it is the sh*ting your posting about.
Well you could stick it on a truck [rostrum with castors] or shove castors on the bed legs. But being a hospital bed it would be mobile anyway?

Will they loan you a gurney?  Gurney's are much lighter than real beds, moveable, and have the side bars--to give it that real hospital look.  Also scaled much smaller for a smaller stage.

Actualy just checking out your website & looking at the the weight there would have been on whole structure during 'all for the best', I think you may be being over worring;-  http://mjct.org/sitebuilderImages/All%20for%20the%20best.jpg
As the weight of the hospital bed would be spread over about at least 18 square feet. even if it was a fully nechanised bed with automatic drive posion motors fitted.
Looking at the stage deck, wich looks like being T&G flooring & the the thickness of the stage flooring, on the  over hang edge on the apron. I believe you could drive a car over it.
However you know your space & structual condition of the stage, ultimatly you have to assess the risk, as in duty of care.
So I will pull my head in!
To produce the bed. Basicly all you need is either an ordinary bed, mounted on a riser [rostra] to give the reqired height. Or make a 6' x 3' rostra & tart it up with a head & tail boards. I'm sure you could find something suitable fosicking about a Op Shop or salvage yard, if it is an old style Iron Com bed, You might find you have risers/rostra you can utalise.
However you might find  a friendly builder who could quickly check out the stages structure for free or a couple of comps. Maybe one of the parents may be qualified to check it out?
Hope this helps  janice.
Chookas

honestly if your stage couldn't hold up a hospital bed I'd frankly say you have bigger issues than what else to use. Not sure I'd want to act or put scenery on that stage.