1) For your first question, please check this website:

http://www.sifma.org/research/statistics/market-sector-statistics.shtml#credit

It lists all major US bond Market Sector Statistics. You can find all 2008 US issuance data.

2) For your second question, its very hard to get, 'cause there is no central place/agency to report such data as its very diffcult to collect these statistics for following reasons: a) too many buyers b) very high turn-over, that is, the bond may be buy-and-resold several times c) certain instituional investors (e.g. hedge funds) don't publish holding.

I can tell you some common bond invest strategy for certain inst. investors in US:

a) Bond mutual fund,insurance company and pension fund usually buy investment grade bond/ ABS (Asset Backed Security) AAA as some regulations required;

b) Hedge fund, Investment bank may buy high risky bond/ABS. 

Hope it will help you!