I think Alt codes are more complicated than you know.
First try looking around the Unicode site, particularly the charts at http://unicode.org/charts/ and http://unicode.org/charts/symbols.html , the name index at http://unicode.org/charts/charindex.html , and the Help at http://unicode.org/charts/About.html . Unfortunately these charts only show the hexadecimal Unicode code values.
But, presuming you are using Windows, you can download Babelmap free from http://www.babelstone.co.uk/Software/BabelMap.html . Babelmap is a utility which (among other things) allows you to see both the hexadecimal and decimal value of every Unicode character.
Each Unicode character each has a unique hexadecimal value usually indicated with a preceding “U+”, so that the letter “A” is U+0065 and so forth. Accordingly each hexadecimal value can be translated into a unique decimal value (well, really into the same value expressed in hexadecimal) but that decimal is not usually provided. You have to convert to decimal. yourself, or get Babelmap or some other utility or calculator to do it.
Now normal Alt codes on the PC are entirely different and are connected to the legacy 8-bit character sets, not to Unicode.. You hold down the left Alt-key (or you can also use the right Alt-key on some machines) and if Num Lock is on, you can enter a value through the numeric keypad while the Alt-key is down, but only a value from 0 to 255.
If you begin your value without a leading zero, the computer will output the Unicode character that corresponds to the same character in your current DOS 8-bit character set. If you enter the value with a leading zero, then the computer will output the Unicode character that corresponds to the same character in your current Windows 8-bit character set.
That is, entering either 65 or 065 should usually produce “A”, as that will usually be the same in both sets. But entering 198, for example, will produce different values depending on whether you enter it as 198 or 0198. On my machine it produces "ã” (from DOS code page 850) without leading 0 and produces “Æ” (from Windows code page 1252) with leading 0.
But these are NOT intrinsically Unicode values, though some of them will be the same as the Unicode values. These ALT decimal values are the values of your current 8-bit character sets in DOS and Windows, not intentionally the values of the corresponding Unicode characters.
And if you enter a value greater than 255, then the output wraps, that is entering 256 will produce output as though you entered 0, 257 will produce output as though you entered 1, 258 will produced output as though you entered 2, and so forth.
Microsoft Office has a different Alt method in which entering characters with a Unicode value greater than decimal 255 (hex FF) will cause the computer to produce the proper Unicode character. Accordingly, what you have to do to get an Alt code that works with Microsoft Office is to find the Unicode character you want to insert, transform its value from hexadecimal to decimal (perhaps through Babelmap) and then enter that decimal value.
See http://www.georgehernandez.com/h/xComputers/CharacterSets/Shortcuts.asp for another discussion of this confusing situation.
In short, there are no Alt codes that work the same for Unicode in every application (which is one reason you have been unable to find them).
You can download the Quick Unicode Input tool for free from http://www.cardbox.com/quick.htm . This will allow you to enter any Unicode value in Plane 1 either in hexadecimal or decimal using the left ALT key and the numeric keypad, or using any key if you are entering a hex value.
(Note that this utility does not work properly under Vista if you set it to start up automatically when you boot. But it works fine if you start it manually after you boot.)
I recommend you try the Quick Unicode Input tool.