PINTREST has awesome ones!
If you could get your hands on old barrels and make sure they're safe, with nothing sticking out, they make a lovely jump if you make a little dip to sit them in.
We also used tree trunks, an old butchers table and telephone poles cause my brother was pretty nifty at woodwork so we made them all ourselves!
I use tyres too! You can make so many different jumps depending on the size and which way you arrange them! We used to slide small ones onto a pole for a handy little upright jump
I use tyres, in the ground and out :)