South Shore Ready Mix manufactures a number of different sizes and shapes of patio blocks.
One of which will suit your needs.

Patio Block Sizes

SIZE	DIAMOND	EXPOSED AGG	LEAF	WITH WIRE
RECTANGLE
12" X 24"	X	X		x
15" X 30"	X
18" X 18"	X	x	x
24" X 24"	X	x		x
24" X 30"	x	x		x
ANGLES
24" X 22.5 DEG	x	x
24" X 45 DEG	X	x
24" X 24" TRIANGLE	X	x
30" X 45 DEG	X	x
ROUND
18": ROUND	X	x	x
20" ROUND	X
24" ROUND	x	x

Metric measurements - 12"/30cm;   15"/38cm; 18"/46cm;  20"/51cm;  24"/61cm;   30"/76cm