The Japanese radio manufacturers (Icom, Kenwood, Yaesu) use Japanese or Eastern Asian
manufacturers (Toshiba, Sanyo, NEC, Mitsubishi, Panasonic, Sony, etc.) for supplying OEM components.
These Eastern Asian manufacturers use the Japanese Industrial Standard (JIS) for transistor and diode part numbers. The specification is found and outlined in: JIS-C-70121S and 2S are common prefixes.Your 2SK2218 part is: Sanyo N-Channel Junction Silicon FET
Here is the Sanyo Datasheet:http://pdf.datasheetcatalog.com/datasheet/sanyo/dis_pdf_e/2SK2218.pdf
In North America, our manufacturers use the Joint Electron Devices Engineering Council (JEDEC) numbering. 1N and 2N are common prefixes.
Earl Andrews, VE3AB in Elliot Lake, Ontario - Canada (NE of Sauté Saint Marie) has been acquiring a number of surplus / obsolete transistors used in amateur radio equipment, especially for Yaesu.http://www.earlandrews.com/index.html
NOTE: Earl is finding a 20% FAILURE Rate (parts) with Chinese/eBay vendors.http://www.earlandrews.com/dgmosbadagn1.html
Dual-Gate MOSFET Shootout, the 3N211 winshttp://www.earlandrews.com/dgshootout.html