You can grow them by seed or by cuttings but, I prefer going thru the driver thru and getting them faster and bigger. You may have to investigate online who sells them. It could be a company or a plant-group-society raising funds. Companies might have a website. The organizations would probably do this in Spring if they follow the models over here. There are forums for that kind of thing in GW too.

The important things for you would be to match the hydrangeas to the climate in your area. Start with a few paniculatas which are hardy, usually to zone 3. Some names that you may see here are Kyushu, Limelight, Little Lime, Pink Diamond, PeeWee and Quick Fire (and Little QUick Fire, both of which bloom amongst the earliest of paniculatas), Hydrangea arborescens is usually hardy to Zone 4. Some examples are Annabelle, which plops when the blooms get large or large-wet, so also consider its "cousins" Incrediball, etc

Hydrangea macrophylla may not do well in regions below Zone 6 because the stems will not survive the winter. There are two options in that case. Winter protect the plants or get rebloomers like those in the Endless Summer Series, Let's Dance Series, Forever and Ever Series, etc. These bloom on old and new wood; of course, the old wood will die during winter but the new shoots will produce flowers too, albeit later than if the bloom was from old wood.

Another option: start by asking your mother which ones in her collection will do well in your area. And which ones she remembers your wife liked the most in her visit. Then see if she will mail you cuttings overnight at your expense.