That should be a shotgun, and it will shoot 12 gauge shotshells or slugs, available at any sporting goods store and most department stores. You should check with a gunsmith to determine chamber size. It may also be marked on the barrels, or underneath them, as to chamber length. Some older 12 gauge take shells that are 2-9/16" long. Most modern ones are 2-3/4", and some will take 3". Each length chamber will take any shorter length shell as well.
Lender's royal service # 117709
Have it examined by a competent gunsmith
No known published sn data
Enders Special Service & Enders Royal Service along with Enders Oakleaf were made by Crescent Fire Arms Co. for Shapleigh Hardware Co. of St Louis, MO in the early 1900's. It is not a rare gun nor expensive. Perhaps $200 if in good condition.
Carl Enders, Suhl Germany. Made high quality double barrel 12 gauge shotguns from 1835 to 1890. They had ornate checkering and engraved metal work. Depending on the condition and workmanship the value is between $500-$1150.
Possibly Enders Royal Service? Blue, Hound, Whistler are a few others
I found a set for my Enders Special Service a.k.a. crescent on eBay of all places. It took some time and alot of questions, pictures and measurements but was worth the wait. There are many barrel sets that will fit with a little tinkering.
Being a .410 helps, the condition hurts. Possibly $200. sales@countrygunsmith.net
try www.e-gunparts.com or www.gunbroker.com you may have some luck there.
Not readily. You'll find that parts will need to repaired or made by a gunsmith.
try john gunderson 518 668 2221
Complete and in working condition - $200-250. Broken or rusty - 0-25