Hey, in the last moment

How to make a non-flying dragon:
1. Mineral warrior template.
2. Rattelyr don't have a wings. And chole dragon have tentacles for wings.

How to make a non-casting dragon:
1. The Nameless template takes away spellcasting and SLA.
2. Make it too young or dimwitted dragon.
3. Planar dragons don't have spellcasting at all.

The last thing - if you have a melee party, give them a "melee" dragon For example, dragon-war hulk or frenzy berserker...

If you want to make encounter a bit easy to them without under-CR dragon, you can give something which, while heightening the CR, doesn't do much for actual power. Such as NPC class levels or stacked half-dragon templates...