Your best bet is to contact Daisy directly. Daisy offers a free service to tell you more about you old Daisy. The Model 21 was made between 1968-1972. Sears Version was made in 1968 only See the link below
Are you aware that the model 25 is in production again. There are 21 different variations of the model 25 before the new one came out. So here is what I suggest. Daisy has a service to evaluate older Daisy air guns. See the link below
To find out how many were made I suggest you contact Daisy Customer service and ask them directly. (see the link below) I do have this information; There were two different models of the Side by Side. The model 21 made between 1968 - 72 and the model 104 from 1938 - 40.
I would start with Daisy air gun company. See the link below. contact Customer service.
The Daisy model 21 took .175 BB's, today's BB's are .177. The model 21 is a rare and valuable double barreled air rifle. They were made between 1968-72. An average value for one in good shape, and still working, is around $400 to $525. In like new condition it is worth $800 Personally I would not play with it or damage is in any way.
daisy is older, daisy is 21, peach is 20 though peach has had mroe experience travelling the stars (peach is actually rosalina by the way)
This could be a very valuable air rifle. If it's the Daisy side by side model. In excellent condition it could be worth between $800 and $1,100. it was manufactured between 1968 - 72. I suggest you go online to gunbrokers or gunsamerica and advertise it there.
I assume you are asking about the "Daisy model 21 Side by Side BB rifle". This model went out of production in 1972 so it would be very hard to locate one. You could have a custom one built ( search the web for "Custom airgun stocks") or locate a shop that repairs air rifles. See the link Below.
Daisy has made 2 double barrel models. The model 21 in 1968 and the model 104 made between 1938-40. BOTH are very valuable. Unfortunately It's not possible to estimate the value because there is no description of the rifle given. Please state the condition of the rifle. Very Good, Good, Fair or Poor. Does it still work?
Try Numrich Arms, they have a website and a lot of used parts.
In order to give you an answer it is necessary for you to give a description of the rifle. is it still working? Rate it as poor, fair, good, very good, or excellent. Then it is easier to give you an estimate of value.Or you can go up on the "Daisy" website and click on Daisy "Museum," at the bottom of the Daisy Museum page you will find "Do you want to know more about your old Daisy"Open it and follow the instructions.
The model 21 side by side was made from 1968 to 1972. One in good condition is very valuable, but finding parts for it may be hard. However there are individual shops that repair antique air guns. I suggest you look on the web for "Air Gun Repair" and locate a shop near you to have it repaired. Or you can see the link below.