first thing you should do is try to contact the author, and ask if he can provide you with the icons, this would make life easier. if that fails, try using gfxreplacer to extract the icons from the vkp, i've found it often won't work tho. another option is to apply the vkp patch to the correct w850 firmware file (using something like
v-klay), then using imgtool db2020 to extract the icons from the patched firmware.