I need to give thanks for someone's post on this forum about how to make your own raised grid. Below is a picture of mine.
Today I bought a grid the diameter I thought would fit in my dome, and then used 4 6" bolts, 12 washers and 12 nuts. Two washers and 1 nut secure each bolt to the top grid. Then near the bottom of each bolt 2 bolts secure one washer to serve as the foot resting on the lower grid. I haven't used it yet, but it seems to be sturdy, and is easily removed anytime during the cook. Hopefully I'll be as pleased once I use it. Thanks again to whoever shared the idea!