I would like to suggest that the solubility in HF can be increased by using a mixture of any ammonium fluoride/HF mixture in non aqueous solvents. try different composition of both then you can increase the solubility and then use any extraction techniques to separate the ammonium ions. crystallization of remaining may produce indium fluoride. this is only my imagination.

Best wishes

Since aqueous solutions are needed you probably are going to form the hydrated form in most cases.. here's a procedure that i found to work up to 5g.

In2(SO4)3xH2O (3.3 g, 6.4 mmol) was dissolved in hot freshly distilled water (50 mL). A concentrated solution of NaOH (5 mL of 10 M) was added until a white solid precipitated. The solid was filtered off and washed with water. The solid was then suspended again in water (10 mL) in a Teflon beaker (important to use teflon container at this stage) and HF 40% (5 mL, 115 mmol) were added, giving a clear solution. After several minutes a white solid started to precipitate and the mixture was allowed to stand overnight. The solvent was decanted off and the solid dried in vacuo. Yield: 0.89 g, 62%.

Thank you for your valuable answers. @Fady Nahra, the process you mentioned seems logical. I will give it a try and will let you know the result. Thanks again everyone!