Another time and maybe day also I will put a post to links to online sites at which electronic parts can be bought, but for now:

To find information on semiconductors (Transistors, ICs, Diodes) Use the search engines from below and or just use any search engine such as Google.

http://www.datasheetcatalog.com/
http://category.alldatasheet.com/index.jsp?semiconductor=Electronic
http://www.datasheetcafe.com/
http://www.standardics.nxp.com/
http://www.datasheetarchive.com/
http://www.alldatasheet.com/
http://www.alldatasheet.com/?gclid=CI_FgYSFvZECFQU6awodV0E3DA
http://www.supplyframe.com/campaign/?s_kwcid=datasheet|1054685892&gclid=COSznqyFvZECFRIUagodOhYKCg
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To Find Semiconductors try:

http://www.circuitworld.com/subpage/semicond.htm

And also try Google or other search engine.

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To find any electronic part(s) whatsoever, use a search engine such as Google, AltaVista, Yahoo! or some other one.
Those above are mostly for finding semiconductors information.
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Best way to learn how to find parts and their data is to practice with the search engines.
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Good luck!

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To get some practice enter, but only one part search at a time:

LM555

LM741

LM324

LM380

LM386

2n3906

2n3904

2n2222

CA3130

LF355

TL084

TL082

BC107

BC179

BC109

BC159

NTE159

BC177

BC560

BC549

BC559

1N34A

1N60

1N914