For 800Hz, you could try the Peavey CH-3 or JBL 2370. Martinelli makes a 17" wood horn that's gorgeous and sounds great too.For 500Hz, you'll need to move to a 2" driver on a horn like the JBL 2380 or Eminence T12000. Martinelli makes a 21" horn for 2" exit compression drivers that's real nice.
You might also consider Altec 811 and 511 horns. The 811 is for 800Hz up and the 511 is for 500Hz up.