Another great mellotron ap is Wusik Eve. As with Sampletron, allows the range beyond the 32 note limit above and below and extensive mix and match, editing capability. Mellotrons and a lot more. Always some fire sale going on, so the $79 never applies. Demo craps out after 30 minutes, but will give you the idea.
http://www.wusik.com/ww/products/wusikeve For pure mellotrons, there are several freebies that can do the job well. Also free downloads of wav samples that can be tossed into a sampler. Internet search needed. Death of Sampletron is not death of the mellotron, and another thumbs up for MTron Pro.
John