I'm sorry that your question hasn't been answered. I'm not aware of a solid lower case replacement for your MacBook but there are new replacement lower cases available that should last a long time, such as this one: http://www.ebay.com/itm/Eathtek-New-Lower-Bottom-Case-Cover-for-Macbook-Pro-13-Unibody-A1278-2009-2010-/201921898456?epid=864809777&hash=item2f037ba7d8:g:1EsAAOSwYlRZFMwu
There are also used lower cases on eBay in good condition for around $20. iFixit may sell them here on their site as well.