You can search for a House Report number within the Internal Revenue Acts of the United States. Begin your searching by entering the Taxation & Economic Reform in American Parts I & II database and click on Internal Revenue Acts of the United States, 1909-1950 (Carlton Fox Collection). From here choose the House Report Number option from the drop down menu. You do not need to input the prefix H. Rep., only the document number itself.
Example: Search for H. Rep. 75-1546