Myrtus Communis from Seeds

Rightly or wrongly, when I see seeds as well as plants offered for a single species, I assume that the seeds are difficult or troublesome to get going. I would like to cultivate some Myrtus communis but have been unable to get any information on how difficult they are to germinate and grow. I'd appreciate any information you might have.

You are right in some cases, but by no means are you right in all cases. For example, we offer both because many people simply do not have the patience or skill to grow plants from seeds. Or, because the plants in question take too long to mature in areas where the growing season is short. Or, because people who only need a few plants buy potted herbs while others who need hundreds or thousands of plants can only afford to buy seeds.
Take lemon balm. It is very easy to start from seeds, but we offer plants which many people prefer to buy. Myrtle (Myrtus communis), on the other hand, does happen to fit your thesis: it is somewhat difficult to start from seeds because the seeds are slow to germinate and slow to develop into a good size. Myrtle seeds may take two years to reach 30 centimetres in height.
Myrtle seeds have a hard seed coat which may impede germination. We have not tried any pre-treatment to speed up germination, but a green thumb with a knack for experimentation might try nicking the seed coat with sandpaper or a sharp knife and soaking in water overnight before sowing. Bottom heat of 30 degrees Celsius is beneficial also. Be prepared to wait 30-90 days for germination to occur, and don't expect more than 40-50% germination.