Specimen bottle / boiling tube rack for autoclave

I've got a Prestige Medical Classic autoclave (I know, lucky me). I was just wondering if anyone had any suggestions for what to use as a rack for specimen bottles (about the same diameter as boiling tubes) - I'm forever knocking them over when filling and emptying the autoclave.

All suggestions gratefully received...
Short of buying some metal racks for them have you tried standing them up in large beakers?
Not sure on the dimensions of that autoclave but you'll get 6 boiling tubes in a 400ml beaker
You are looking for universal bottle or McCartney bottles racks

Yep, I found racks similar to this, its a bit of a round hole, square peg problem. It would have to be a small square rack which would only fit in 9 tubes. If I put them in loose I can fit about 25+ tubes in which is great when they are holding each other up, but as soon as you start unloading them they all fall over. Someone once suggested using a z type test tube rack on its side, but they are very deep so fiddly to get stuff in and out.
Thank you for all your ideas. I can report back that using 3 x 250 Azlon beakers I can fit 12 bottles in and I can then feed 8 more bottles in the gaps around them to give me a perfectly acceptable capacity of 20 bottles in the autoclave.
This is exactly what I have been looking for as well, I am assuming that you stack a few in an offset pattern to get multiple layers?