Hello and welcome to the club, Regarding the manual only one i've found is this.
http://www.ebay.co.uk/itm/Lexus-GS300-430-Workshop-Manual-Technical-CD-1997-2004-/321236829250?pt=UK_CarParts_Vehicles_Manuals_Litterature_ET&hash=item4acb350442
covers everything and is well worth the money. I have a service schedule for the is300 which has same engine, if you pm me your e-mail address i will send you the pdf.