Take it to a gunsmith. He has much better availability for parts. Western Field was a Montgomery Wards brand, so there isn't going to be a lot of collector interest.
Numrich Gunparts.
Go to Numrich Gun Parts Corp.It will be helpful if you know the original maker of your shotgun,as all guns that were made under the Western Field name(Montgomery Wards) were made by outside firms for Montgomery Wards.If you list the model number of your western Field shotgun,this can be cross referenced to the original maker and help you get the right model of shotgun to locate parts.
You can find parts for many westernfield shotguns at Numrich gun parts. WWW.e-gunparts.com
who made montgomery wards bolt action 20 ga shotgun with a clip.
There are several types of gun stores that sell parts for different types of shotguns including models by Western Field. There are also online retailers like Amazon that sell these parts.
your western field shotgun was made for Montgomery wards by mossberg.There model number was 395K.I would look at numrich gun parts corp, or maybe E-gun parts,Both are on the web.
I tried to find that 15KX, but it doesnt seem to exist. Could this gun possibly be a bolt action shotgun with a clip? If so, its very possible that its a Western Field 151X and the number 1 looks like a "K". The Western Field 151X was made by Kessler Arms in Silver Creek, NY. The shotgun was only made from 1951 to 1953. The Gun Parts Corporation in Hurley NY may have parts and more information for you.
it is a mossberg model 500a . the code for western field is pretty easy once you look at a few of them. parts are very easy to find. eBay if you are feeling lucky. or www.e-parts.com for a great company. your shotgun is very popular and there are lots of upgrades out there for it. good luck
Numrich gun parts
Numrich has a cross reference list (http://www.e-gunparts.com/crossref.asp). It seems that your shotgun is the same as a Mossberg 500E. I have the same gun and ordered parts from them. Here is the site that has a parts list. http://www.e-gunparts.com/productschem.asp?chrMasterModel=0840z500
The Western Field 550 series were produced by Mossberg for Montgomery Ward. Basically it's a Mossberg 500 and as far as my research and experience with them goes (I own a 550AB in 12 GA and a 550ED in 410 GA), all parts are interchangeable though I've only ever put a Mossberg barrel on my Western Field.
I think your shotgun was made for Montgomery Ward by Savage as their Model 620A. SOME parts are available from Numrich. These were made starting in the mid 50's, and are about $150, depending on condition.