I definately wouldn't discount motherboards with real-time clocks; there are some good ones.
Your other option, besides the hackery, is to desolder the RTC. I've done this successfully on numerous motherboards. It makes for a cleaner, more preserved look to the motherboard.
The 12887 real-time clock is still sold and manufactered new. Digikey, for example, sells new unit (with new batteries). They typically last 15 years. I've seen these RTCs die in 11 years, and sometimes last for even 18 years.
New DS12887+ Real-time Clocks made by Maxim can be found here (DS12887+),
http://search.digikey.com/us/en/products/DS12 … 87%2B-ND/956874
If you are going the desolder route (be sure to use a solder sucker and the appropriate desoldering temperature/tip), you'll also probably want to solder in a DIP socket that in another 15 years, you do not need to desolder again. Instead, you'd just replace the RTC like you would a DIP BIOS or cache, that is, by prying it up with a screw driver or IC puller.
The proper DIP-24 socket can be found here (4824-6000-CP),
http://search.digikey.com/ca/en/products/4824 … 5467-ND/1133620
If you do go for the RTC hack-job route, and do not have a socketed RTC, the hack job will be a lost easier if you desolder your RTC, and solder in place the DIP-24 socket noted above. If you don't have any 2032 coin cell battery holders, digikey also sells them (120591-1),
http://search.digikey.com/ca/en/products/1205 … 99328-ND/289426
Note that Digikey is just one supplier I choose for this example because I like their search function. A lot of these parts, once you know the part number, can be found cheaper on futureelectronics.com, mouser.com, or newark.com, to name a few.
Happy hacking!
Plan your life wisely, you'll be dead before you know it.