Harvesting yeast is pretty easy, just a few steps involved, for a traditional mead it'll be even easier than with beer or a flavored mead.
1. before you rack your mead into the secondary.
A. Boil about a gallon of water for 10 minutes then let it cool down to the same ambient temp as your mead.
B. Sanitize (either with sanitizer or by putting it in the water while it boild) a couple glass pint jars and lids or similar size sealable container.
C. Sanitize a gallon size container like a glass fermenting jug and funnel.
2. Rack your mead into your secondary obviously get as much out as you can
3. Add a gallon of boiled/cooled water back into your primary and swirl it around really well just to make sure its a good homogenious slurry.
*If you made a flavored mead continue to step four, if a traditional mead skip to step 5*
4. Let the slurry sit for about an hour, most of the unwanted trubish stuff will settle all the way to the bottom, most of the yeast will be in suspension still.
5. Gently pour into the santized extra container, slowly so as to leave the majority of the crap you don't want in the primary, there will be definite stratisification lines and a color difference, you just wanna leave most the useless deposits behind.
6. pour the new slurry, either from the extra just, or if tradition, from the primary into the pint jars, filling to the very top (minimize oxygen)
*In about 24 hours you will see the yeast happily settled into a 1/4 inch or so of a yeast cake at the bottom of the jar and clear liquid resembling original mead above it.
7. Place jars in fridge for a couple few months until you make a similar mead again, idealy you'll use this yeast in a mead that has same honey as the original.
8. When ready to use, take out of the fridge 1-3 days before you are going to make your mead, pour or rack off the liquid and make a starter out of the yeast.
Ive mentioned doing this in other posts and it seemed to upset some people that were worried about stressing the yeast, this process is done extensively in beer making, often brewing 2-6 batches of beer from the original pack of yeast, Ive read of some people that have used that yeast over and over for a year or more. I have done this with mead, actually used the same yeast to repitch into the batch it came from with some extra nutrients to dry it out more, it worked well.