Crosman no longer has parts for this rifle. But there are independent companies that repair older air guns. Crosman offers a free service to locate these shops.
See the link below.
As far as I know there is no Crosman model 88. Daisy made a model 88. I've attached a Link to Crosman's list of Owners manuals for all their rifles. You are welcome to look at it and try to find a Crosman model 88. See the link below.
I believe Crosman never made a model B661 (But I may be wrong) I've searched the web and 5 different Catalogue Airgun books and can not find any reference to a Crosman Model B661.
Crosman still has parts available for this model. See the links below for the parts manual and Crosman customer service.
Crosman still has parts available for this model. You can order directly from them. I've attached a link below of all the Owners and parts manual for Crosman rifles. (it's a Crosman web page) Find your model and open the parts diagram Then call Crosman customer service and order your needed parts. Crosman is spelled with One "S"
I can find no record of Crosman ever making a model 3101 but they did make a model 3100 from 1987-90 See the link below for the full list of old Crosman models
You can find one from Crosman. They still have parts for this model. See the 2 links below.
Crosman has the information online. See the link below
Crosman Corp still has the Owners Manual online. You can find your manual here. see the link below
Crosman offers a free service to locate repair shops that repair older model Crosman airguns. see the link below.
I have absolutely no information on a Crosman model 143. Are you sure it isn't a model 140 or model 147. I even searched the net and can not find anything on a model 143.
You can find it on the Crosman web page. The JC Higgins model 180 was made by Crosman Air guns. See the link below
There are a few places you can find a Rear sights for a Savage Model 120. The most popular place to look would be online or a gun store.