It's hard to be nursing the oldest child you know. I was in the same position when my twins were young. My twins nursed until they were 5 1/2 and 6, and I really didn't know anyone else who nursed that long IRL. I had a couple of friends through LLL who'd nursed for as long, but their children were older and weaned by the time we met. It definitely felt lonely. It made me really glad to have the Internet. Besides these boards, there are extended nursing groups at the LLLI forums and there is a Yahoo group for extended nursing. There are other moms out there, it just takes some persistence and creativity to find them!
My IRL community has grown since then and I have a lot of friends nursing older children now. LLL has definitely been the main source, not just my local group but becoming involved in the greater area to meet more moms and Leaders. We also homeschool and there is a lot of crossover - the parents who followed their children's needs as babies and toddlers often end up homeschooling because we can't see starting to ignore their needs and hand control to strangers simply because of their age (just like we don't wean arbitrarily based on age). So I've found a lot of friends with older nurslings, or who followed that route, in the homeschool community. And an Attachment Parenting group started up in the next town, so we've met families through that. Then, having DD#2 at home with midwives connected me to the homebirth community, with another group of moms following their children's cues.
After DD#2 was born, we had breastfeeding challenges due to her tongue and lip ties, and oversupply. It was SO different than when I had my twins, and had no community. I had midwives visiting my house every few days, friends who were either experienced bf moms, LLL Leaders, or IBCLCs (or all 3!) calling me and coming over to check in on us. We found solutions and resolution much faster, constant support, and never ever a suggestion of giving bottles or formula, even though she lost far more weight than expected at first. And now that's she's 2, I haven't heard a suggestion yet that she should be weaned. . . all my friends expect her to still be nursing!