The 500-MHz frequency counter was dropped from the 1992 Handbook
because many of the parts had become difficult to locate. (We really
did try hard to select components that would be around for a while!)
These are the sources we were able to locate. If you find that any of 
these sources have "dried up", please send email to mtracy@arrl.org 
(Michael Tracy). 

ICM-7226: Digikey, cat# ICM7226AIJL

11C90: Ramsey Electronics , Debco Electronics, Hamilton Avnet (11C90DMQB
$43.00 each - $25.00 minimum credit-card order)

74S160 (substitute 74F160, 74HCT160 may work, 74LS160 good to 350 MHz): 
Digikey, cat # 74F160APC, Ocean State Electronics, cat# 74HC160, Jameco,
cat# 74S160, cat# 74HC160

LM360: Digikey, cat# LM360N, Ocean State Electronics, cat# LM360N

MAR-6 (substitute MSA-685), Microwave Components of Michigan (MCM)

DC Electronics, PO Box 3203 Scottsdale, AZ 85271, (800) 467-7736
Digikey, 701 Brooks Ave, Thief River Falls MN 56701, (800)-344-4539,
Hamilton Avnet, 1-800-332-8638
Jameco, 1355 Shoreway Rd, Belmont CA 94002, (415) 592-8097
MCM, POB 1697, Taylor MI 48180, (313) 753-4581 evenings only
Ocean State Electronics, POB 1458, Westerly RI 02891, (401) 596-3080
Ramsey Electronics, 793 Canning Pkwy, Victor NY 14564, (716) 924-4560
Debco Electronics,4025 Edwards Rd, Cincinnati OH 45209, (513) 531-4499

The members and HQ staff would like to thank the following people for
their contributions to this information file:

KA1CV N2TTE

Send any additional information or changes to mtracy@arrl.org. 

73 from ARRL HQ.