Take a look at the catalogue entry for "full horns". Backstrips are £1 per item more expensive, having handling + cutting included in the price. You receive the "back strip" material with it's natural internal and external surfaces, ready to dress down and dimension. These are lighter in weight to send overseas, so saving on shipping costs and with the cutting already done for you. Typically a generous 50mm in width, and your specified length on the outer arc.
Photo shows backstrip removed by bandsawing from typical , suitable horn. We can forward either "just" the strips ( to save carriage costs ) or strips plus offcuts where carriage costs are quioted ahead of payment and approved by you. If you want the leftover material also sent....mention this in the comments field at the end of the ordering process please.
80 - 90cm horns are RARE and take time to find in bulk stock - thus a premium is payable and the order may take A FEW WEEKS to enable selection from bulk stored material.