I don't think you need to worry too much about them finding each other because most of your survivors will die, and I think there is almost no chance that the number of survivors will assure the survival of humanity, even if they miraculously find each other. You need a much higher survival rate, which will affect communications and subsequent ability to find each other.
Approaching this only from a medical perspective, given your scenario (1 in 100K survive without restriction by genetics, age, location, etc. and loss of electricity/technology), about 12,500 will be aged 9 and under. Those under 5 will die in days from lack of water; those from 5 to 9 might live longer, but will likely die of disease, dehydration, exposure, malnutrition, etc. unless found by adults, so let's be generous and say 200 live and can someday integrate.
6,000 will be elderly (between 65-99) and will be well more than half women. While they will be helpful repositories of knowledge and can do light work, they cannot do too much, and their life expectancy will be dramatically reduced.
12,000 will be 10-19 years old. Most of those will have little skills or resources to stay alive (they will not know how to forage, let alone farm.) They, too, will be subject to disease and dehydration from unsanitary water and conditions (there are an awful lot of decomposing bodies around), and later by exposure. Being generous, let's say about one third will live more than 9 months. that's 4000, with about 2000 females. About 800 will be of reproductive age.
The golden number here is 28,000. That's the number of people alive between the ages of 19 and 45 (not inclusive). 998
Half will be women of childbearing age. With the 10-19 year old surviving females, (14,000 plus 800) that leaves 14,800 women to repopulate the earth under adverse conditions. Of these, 2% will never conceive (296) and 10.5% will be unable to conceive after having one child (1,554) Of those who do conceive the first time (14,504), one in 100 will die from each pregnancy (the rate in underdeveloped countries) from postpartum hemorrhage, eclampsia, obstructed labor, and sepsis, (145 women) with the rate being 1 in 16 chance of dying from childbirth in her lifetime.
If all the females of childbearing age find males to reproduce with, after the first year of mating (not taking into account a spontaneous abortion rate of 20% before the 14th week), ~14000 babies will be born (half girls), 10% of the women will become infertile, and women will continue to die in childbirth: ~12930 women will be left for a second round. Miscarriages will increase due to decreased nutrition. Women will not have a baby per year in even the best of circumstances; the highest average number of babies per female in developing nations in the 1980s was 8.3. In the worst of circumstances, it will be much less.
In other disasters where a population was forced to become agrarian without technology (e.g. the Cambodia under the Khmer Rouge, after the initial killing of ~3% of the population, close to 25% of the population died in only 4 years (disease, starvation, overwork), and that was in a temperate climate. Your people have to travel to better climates by foot or animal. Think Oregon Trail. Mortality is very significant. A best guess scenario might mean the loss of about 3500 women in maybe 5 years, leaving ~9400 women capable of conceiving.
So, under ideal circumstances of every female mating every year, with the infertility, maternal death (and not even taking into account infant mortality, (which, as in developing nations will be significant), and an overall death rate of 20% in the first 5 years only, you'll be left with too few women and children to come close to repopulation.
If they are spread across the globe and must travel to find each other, the numbers shrink to a small fraction of the best case scenario. 838