Thanks everyone. I'm waiting for a reply from Daniel, an herb supplier who has lovage on their product list. I notice that Richter's will be offering Lovage plants in the spring! I saw a photo of chinese celery and was wondering if it was the same thing?
T&M varies from year to year, selection-wise. I'd try Richter's for seeds or plants. It's a tough and easy to grow perennial. No, it's not the same as Chinese celery--different scientific names if you check 'em out.
I stopped growing it indoors during the winter because it was very susceptible to white fly or aphids (very tender and succulent). I use celery heart as a substitute, but may try celery seeds for some things as suggested above.
The old timey way to preserve lovage for winter was to candy the stems. I didn't do any this year, the result is great fun, a bright almost electric green in colour and that subtle almost anise flavour. I've seen candied lovage used as a cocktail straw as it is hollow.
Maybe dried leaves now but I've never seen it for sale fresh. I grow it in my garden. It's a very old school herb. You might have some luck in well-stocked Italian grocers(Woodbridge?) with dried leaves or seeds. Celery seed comes close, flavor-wise.