I just placed my order for Runner 250 spare parts on Aliexpress. For convenience, I ordered all the Walkera parts from a single seller, TomTop RC Store, awell established R/C parts seller in venues including Amazon, eBay and Aliexpress.
Runner 250 Advance upgraded battery tray, part number 250(R)-Z-04, $4.72
Runner 250 Advance upgraded rotor set (two pairs), part number 250(R)-Z-01, $5.08 (if you prefer the original Runner 250 rotors, they are $5.56 for two pairs)
Runner 250 Advance camera and headlight guard (not included with the original Runner), part number 250(R)-Z-05, $2.56
Runner 250 original landing gear (set of 4), part number 250-Z-09, $3.23
Total order was $15.59, free shipping, 15 day delivery time.
At a minimum, it's a good idea to grab at least a set of rotors, but I also included the landing gear for three bucks knowing that it's just a matter of time before I'm skimming the ground for some hot FPV action and snag up on a rock or something and snap off one of the landing gear. Same reason I added the camera/headlight guard. Better to snap a $3 hunk of plastic than to break the power board or camera lens.
If you've got a few bucks to spare, I encourage you to take advantage of the Aliexpress anniversary sale and grab a few spares now, before you break something and are grounded for two or three weeks waiting for replacements.