Please understand that there are generic parts and custom parts. For generic parts, search for the number printed on the chip, avoid an isolated group of four digits, for example "9823" which is probably a date code, week 23 of 1998.
If you can't find the part number in a search, look for a manufacturers name or logo and try their web site.
You will find SMD parts, especially ones with 6 or fewer pins are usually codes with a one, two or three character code. These can be very difficult to identify as there is no standardization between manufacturers.
Custom parts are essentially useless, they are made for a specific purpose and to a design known only to the equipment manufacturer. Any specification will be confidential between the designer and the chip fabrication facility and you stand very little chance of finding it out. Unfortunately for you, custom chips are quite cheap to make these days and there are a lot of them around.
Brian.